91 is a natural integer number, after 90 and before 92. It is ninety-one in English form.
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Factorization[]
91 is equal to 7 x 13 or 13 x 7.
Proof:
91 does not end with a 2, 4, 6, 8, or 0, so it's not divisible by two.
It is not divisible by 3, because 9+1 = 10, 1+0=1, and 1 is not a multiple of 3
91 does not end with 5 or 0, so it is not divisible by 5.
91/7 equals to 13, so it is divisible by 7.
Properties[]
It is the 27th semiprime (a number added by two primes).
A triangular number: 13th number, equals to 1+2+3+4+......+10+11+12+13.
A hexagonal number: After 66 and before 120.
It's the smallest number presented as six continued squares: 12 + 22 +...... +62
It is centered cube number.
Uses[]
91 is the number international call of India.