A page of the Numeropedia - the Special Encyclopedia of Numbers
[Calendar] The number of days of the first quarter (January-March) is either 90 for a non-leap year or 91 for a non-leap year.
[Chemistry] The atomic number of Thorium (Th). An element in the Actinide series: Actinium (89) to Lawrencium (103).
[Geology] The 90th parallel (90o latitude line) North (or South) is the North (or South) pole.
[Geology] I-90, the longest major U.S. West-East interstate highway, connecting Seattle, Washington to Boston, Massachusetts, 3163 miles. It is the longest major U.S. interstate highway.
[Language] Prefixes : Nonage-
[Library] ISBN-90 is the International Standard Book Number for books published in Dutch and Flemish.
[Math.] Units for angle measures: 90o = (p/2) radians = 100 grads (grades).
[Math.] The right angle or the interior angles of a square are 90o.
An acute angle is less than 90o.
An obtuse angle is greater than 90o but less than 180o.
[Math.] Sum of 2 complementary angles is 90o. sin(a) = cos(90o–a); tan(a) = cot(90o–a).
[Math.] sin(0o) = sin(180o) = cos(90o) = cos(270o) = tan(0o) = tan(180o) = cot(90o) = cot(270o) = sinh(0) = tanh(0) = log(1) = 0.
sin(90o) = cos(0o) = tan(45o) = tan(225o) = cot(45o) = cot(225o) = cosh(0) = 1.
[Math.] 90 = 01+12+23+34.
[Math.] Two consecutive sums of consecutive numbers: 16+17+18+19+20 = 21+22+23+24 = 90.
[Math.] The infinite sum Sn(1/n4) = p4/90 = z(4), where Sn is the infinite sum which n runs over all positive integers and z(s) is the Riemann zeta function over complex variable s.
1×8+1 = 9
12×8+2 = 98
123×8+3 = 987
1234×8+4 = 9876
12,345×8+5 = 98,765
123,456×8+6 = 987,654
1,234,567×8+7 = 9,876,543
12,345,678×8+8 = 98,765,432
123,456,789×8+9 = 987,654,321
1,234,567,890×8+90 = 9,876,543,210
(start of a new cycle)
12,345,678,901×8+901 = 98,765,432,109
123,456,789,012×8+9,002 = 987,654,321,098
1,234,567,890,123×8+90,003 = 9,876,543,210,987
12,345,678,901,234×8+900,004 = 98,765,432,109,876
123,456,789,012,345×8+9,000,005 = 987,654,321,098,765
1,234,567,890,123,456×8+90,000,006 = 9,876,543,210,987,654
12,345,678,901,234,567×8+900,000,007 = 98,765,432,109,876,543
123,456,789,012,345,678×8+9,000,000,008 = 987,654,321,098,765,432
1,234,567,890,123,456,789×8+90000000009 = 9,876,543,210,987,654,321
12,345,678,901,234,567,890×8+ 900000000090 = 98,765,432,109,876,543,210
... (end of cycle)
[Phone] International telephone dialing code for Turkey.
[Sport] The distance (feet) from base to base (included home plate) in a professional baseball field.
[Sport] The number of edges on a regular soccer ball (truncated icosahedron), formed by 32 polygon pieces (12 pentagons and 20 hexagons) and a total of 60 vertices.
[Sport] The regular time (minutes) for an official match of soccer game: two 45-minute halves.
[Tech.] The “number system” code of an EAN-13 barcode for Austria’s products: 90 and 91.
[Tech.] Octane (R+M)/2 antiknock index rating of unleaded gasoline for automobiles in the U.S.: 87, 88, 89, 90 and 91.
[Tech.] The numbers of automobile gear oil SAE viscosity: 75W, 80W, 80W-90, 85W, 90W and 140W.
[Tech.] The popular Alkaline-Manganese battery voltages for household electronic devices: 1.5V – 3V – 4.5V – 6V – 9V, available in popular sizes: AAA, AA, C, D, G and N. The Carbon-Zinc batteries have additional values: 12V – 22.5V – 45V and 90V. Other values: PP3 – 1.2V – 3.6V – 4.8V – 8.4V for Ni-Cad rechargeables.
[World] The ISO-3166 country code for Solomon Islands (was British Solomon Islands).
[Sport] The isosceles triangle of sides 12-12-17 (inches) at the top of the home plate (whose shape is a non-regular pentagon) in baseball is not quite a right triangle as specified, since 122+122 = 288 < 172 = 289. Its largest angle is an obtuse angle of 90.2o.