91216921 has 2 divisors, whose sum is σ = 91216922. Its totient is φ = 91216920.

The previous prime is 91216913. The next prime is 91216963. The reversal of 91216921 is 12961219.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 87216921 + 4000000 = 9339^2 + 2000^2 .

It is a cyclic number.

It is not a de Polignac number, because 91216921 - 2³ = 91216913 is a prime.

It is not a weakly prime, because it can be changed into another prime (91216991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45608460 + 45608461.

It is an arithmetic number, because the mean of its divisors is an integer number (45608461).

Almost surely, 2^91216921 is an apocalyptic number.

It is an amenable number.

91216921 is a deficient number, since it is larger than the sum of its proper divisors (1).

91216921 is an equidigital number, since it uses as much as digits as its factorization.

91216921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1944, while the sum is 31.

The square root of 91216921 is about 9550.7549963341. The cubic root of 91216921 is about 450.1512594392.

The spelling of 91216921 in words is "ninety-one million, two hundred sixteen thousand, nine hundred twenty-one".