Number 13

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Number 13 in Math.   Number 13      (More Math. pages)


[Astronomy]  The number of known natural satellites of the planet Neptune: Triton, 7 small named moons (Despina, Galetea, Larissa, Naiad, Nereid, Proteus and Thalassa) and 5 recently discovered not-yet named moons.


[Calendar]  “Blue moon” is the rarely-occurred 13th full moon in a year.


[Calendar]  The number of days added to the calendar for any country to adopt to the Gregorian calendar (created by Pope Gregory XIII in 1582 to reform the old Julian calendar) during the 20th century, (since 1700, 1800 and 1900 were not leap years). Those countries are: Russia (Soviet Union) in 1917, Greece in 1923…


[Calendar]  The number of months in a Chinese lunar (or lunisolar) leap year (or intercalary year). The extra month is the first month after the Winter Solstice has no “Principal Term”); it bears the name of the previous month and designated as intercalary month.


[Calendar]  The number of leap years in the B.C. period, after the Julian calendar was first decreed by Julius Caesar in 46 B.C. to reform the Roman calendar: 45, 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12 and 9 B.C. Leap years mistakenly occurred every 3 years instead of 4 years as decreed.


[Chemistry]  The atomic number of Aluminum (Al).


[EECS]  In hexadecimal number system, D = 13.


[EECS]  13(W, KW or MW) is one of standard numerical values for resistors (of tolerance class 5%).  13pf (picofarads) is one of standard numerical values for capacitors.


[Flag & Gov. & History]  The number of equal horizontal stripes of red (from top) and white alternating on the U.S. flag, representing its 13 original states, listed in order of the dates of entering the Union: (1) Delaware, 7 December 1787, (2) Pennsylvania, 12 December 1787, (3) New Jersey, 18 December 1787, (4) Georgia, 2 January 1788, (5) Connecticut, 9 January 1788, (6) Massachusetts, 6 February 1788, (7) Maryland, 28 April 1788, (8) South Carolina, 23 May 1788, (9) New Hampshire, 21 June 1788, (10) Virginia, 25 June 1788, (11) New York, 26 July 1788, (12) North Carolina, 21 November 1789 and (13) Rhode Island, 29 May 1790.


[Flag]  The number of rays of red and gold on the top half of the Arizona state flag, representing the 13 original states of the Union.


[Flag]  The number of stars encircling the state seal on the Georgia state flag, which represent the 13 original states of the Union. It is on the latest redesigned flag, adopted on 8 May 2003, voted in 2 March 2004.


[Flag]  The number of gold stars forming a circle encircling the torch on the Indiana state flag, representing the 13 original states of the Union. The other 5 stars inside the circle are for the next states ahead of Indiana joining the Union and the largest 19th star above the torch for Indiana, the 19th state of the Union.


[Flag]  The number of stars in the symbol X of the Mississippi state flag, representing the 13 original states of the Union.


[Flag]  The number of golden stars above the bald eagle on the North Dakota state flag, representing the 13 original states of the Union.


[Flag]  The number of white stars surround the letter “O” in white and red in the blue triangle on the Ohio state flag, toward the base of the triangle, representing the 13 original states of the Union. The other 4 stars are at the peak of the triangle, for a total of 17 stars, representing the 17th state of the Union.


[Flag]  The number of gold stars forming a circle encircling the gold anchor on the Rhode Island state flag, representing the 13th state of the Union.


[Flag]  The U.S. flag is ceremonially folded 13 times; upon completion, it appears as a cocked hat, and the stars are uppermost.


[Geology]  The 13th step of the Colorado State Capital building in Denver is exactly 1 mile high above the sea level.


[Gov.]  In the Great Seal of the U.S., there are 13 stars over the head of the eagle, 13 arrows in one of the eagle’s claw, an olive branch of 13 leaves on the other claw, 13 letters in the phrase “E Pluribus Unum” and 13 rows of bricks in the pyramid.


[History]  Rhode Island was the 13th state to ratify the U.S. Constitution to join the Union, on 29 May 1790. It is the state of the smallest area among 50 U.S. states.


[History]  The 13th U.S. President: Millard Fillmore (Whig, New York, 1850-1853). There was no Vice President.


[Language]  Conjecture: All numbers greater or equal to 13 is honest, that can be described using exactly n letters in standard mathematical English.


[Language]  The only solution for the numerical and English alphabetical equation: TWELVE+ONE = TWO+ELEVEN. The letters are identical on both sides of the equation.


[Language]  Prefixes: Tridec-, Tredec-, Trideca-, Triskaideca-…


[Language]  Triskaidekaphobia (or Tridecaphobia, Tredecaphobia) is the fear of the number 13. 

Generally, arithmophobia is the fear of numbers.


[Language]  Assembly or band of usually 13 witches is called coven.


[Library]  ISBN-0-13 is the International Standard Book Number for books published by Prentice Hall.


[Library]  The number of digits in the ISBN-13 (13-digit International Standard Book Number, will be implemented in January 1, 2007, to match with the “number system” code of an EAN-13 barcode, by adding “978” or “979” in front of the current 10-digit ISBN, where the check digit will be recalculated over 12 digits, instead.


[Measure]  Baker’s dozen, an old informal (or traditional) unit of quality. A typical dozen is 12.


[Money]   The number of stars circling the torch on the U.S. quarter (drummer coin).


[Money]  The number of stars forming an arch beneath the Independence Hall on the U.S. half dollar coin.


[Money]  The number of digits of a credit card or ATM card number is 13 (Visa), 14 (Diners Club/Carte Blanche), 15 (American Express, JCB, enRoute) or 16 (Discover, MasterCard, Visa, JCB).


[Movie]  PG-13, one of 5 basic movie ratings: G (General Audiences), PG (Parental Guidance Suggested), PG-13 (Parents Strongly Cautioned, for children under 13), R (Restricted, for children under 17) and NC-17 (No One 17 and Under Admitted).


[Movie]  Names of TV shows/series or movies: “Thirteen”, “The Alamo: Thirteen Days to Glory”, “13 Ghosts”, "Apollo 13", “Thir13en Ghosts”, “Thirteen Days”, “The 13th Warrior” and “13 Going To 30”.


[Movie]  Names of TV shows/series or movies: “Thir13en Ghosts”, “Ocean’s Eleven” and its sequel “Ocean’s Twelve” and “Ocean’s Thirteen”.


[Tech.]  The ill-fated Apollo 13 spaceship is the only Apollo spaceship that did not land on the Moon (in 7 Lunar Landing missions Apollo 11 to 17). Its trip lasted 7 days, 11-17 April 1970.


[Tech.]  The number of digits of the EAN-13 barcode, a superset of the North America’s 12-digit UPC-version A barcode. They are grouped into: number system (2 or 3 first digits), manufacturer code (variable-length), product code (variable-length, depending on the manufacturer code) and the check-digit.


[Theology]  The number of persons (Jesus Christ and his 12 Apostles) featured in the painting “The Last Supper” by Leonardo da Vinci on a wall of the church Santa Maria delle Grazie in Milan, Italy.


[Trivia]  The 13th wedding anniversary is traditionally named lace anniversary.

Modernly, it may be replaced by furs/textiles (or citrine).


[Trivia]  The starting/youngest age for being a teenager (13-19 years old).


[Trivia]  An unlucky number, as popular belief. (e.g. the infamous Friday the 13th).


[Trivia]  The first footprint on the Moon is measured 13 inches by 6 inches.


[Zip]  The values of the US non-denominated first-class postage stamps and later values, for the first ounce, starting 14 September 1975 at 10¢ to 44¢, in May 2009.  
















Value (¢)



















[Tech.]  A frequency used by contactless smart card technology: 13.56 MHz.

A frequency used by proximity card technology: 125 kHz.



[Measure]  1 mmHg (torr) = 133.322 N/m2 (pascals) = 13.595 Kg/m2.

[Measure]  The standard atmospheric pressure at sea level is 1 atm (atmosphere) = 1,013.25 millibars = 29.921 inches of mercury (inHg).

Units for pressure measures:

1 atm (atmosphere) = 1013.25 millibars = 101,325 N/m2 (pascals) = 1033.227 g/cm2 = 10,332.27 kg/m2 = 760 mmHg (torrs) = 29.921 inHg = 14.696 lb/inch2 (psi) &

1 bar = 105 N/m2 (pascals) = 106 dynes/cm2 (cgs bars).


13 & 14

[History]  The 14th U.S. President: Franklin Pierce (Democrat, New Hampshire, 1853-1857). His Vice President, William Rufus deVane King (Alabama, North Carolina, 1853), was the 13th U.S. Vice President.  There was no Vice President in the period 1853-1857.

The 13th U.S. President: Millard Fillmore (Whig, New York, 1850-1853). There was no Vice President.