Number 91

A page of the Numeropedia - the Special Encyclopedia of Numbers

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[Calendar]  The number of days of the first quarter is either 90 for a non-leap year or 91 for a non-leap year.

 

[Calendar]  The number of days of the 2nd quarter of a year.

 

[Chemistry]  The atomic number of Protactinium (Pa). An element in the Actinide series: Actinium (89) to Lawrencium (103).

 

[EECS]  91(W, KW or MW) is one of standard numerical values for resistors (of tolerance class 5%).

 

[Game]  The number of tiles in a double-12 set of dominoes.

 

[Library]  ISBN-91 is the International Standard Book Number for books published in Sweden.

 

[Math.]  A triangular number (sum of all integers from 1 to 13):

91 = 1+2+3+4+5+6+7+8+9+10+11+12+13 = 1+91+92.

 

[Math.]  A pyramidal number (sum of all squares of integers from 1 to 6):

91 = 12+22+32+42+52+62.

 

[Math.]  The sum s(n) = 14n+2+24n+2+34n+2+44n+2+54n+2+64n+2 is always divisible by 13 for any integer n³ 0: s(0) = 12+22+32+42+52+62 = 91 = 13×7.

 

[Math.]  (Sequence of numbers (10n–9), n > 1):

912 = 8281 = (82+8+1)2 = (8+2+81)2 and 19 = 8+2+8+1

913 = 753,571 = (75+3+5+7+1)3

914 = 68,574,961 = (6+8+57+4+9+6+1)4

915 = 6,240,321,451= (6+2+4+0+32+1+45+1)5

916 = 567,869,252,041 = (5+6+7+8+6+9+2+5+2+0+41)6

 

 [Math.] 

1,001 = 11×91

1,000,001 = 101×9901

1,000,000,001 = 1001×999,001

1,000,000,000,001 = 10001×99,990,001

1,000,000,000,000,001 = 100001×9,999,900,001

 

[Phone]  International telephone dialing code for India.

 

[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.

 

91.44

[Measure]  1 yard = 91.44 cm (centimeters).

(U.S. customary and metric units for linear measures).