91990321 has 2 divisors, whose sum is σ = 91990322. Its totient is φ = 91990320.

The previous prime is 91990309. The next prime is 91990411. The reversal of 91990321 is 12309919.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 91412721 + 577600 = 9561^2 + 760^2 .

It is a cyclic number.

It is not a de Polignac number, because 91990321 - 2⁵ = 91990289 is a prime.

It is not a weakly prime, because it can be changed into another prime (91990121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45995160 + 45995161.

It is an arithmetic number, because the mean of its divisors is an integer number (45995161).

Almost surely, 2^91990321 is an apocalyptic number.

It is an amenable number.

91990321 is a deficient number, since it is larger than the sum of its proper divisors (1).

91990321 is an equidigital number, since it uses as much as digits as its factorization.

91990321 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 91990321 is about 9591.1584806008. The cubic root of 91990321 is about 451.4199116641.

The spelling of 91990321 in words is "ninety-one million, nine hundred ninety thousand, three hundred twenty-one".