31915721 has 2 divisors, whose sum is σ = 31915722. Its totient is φ = 31915720.

The previous prime is 31915711. The next prime is 31915727. The reversal of 31915721 is 12751913.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20430400 + 11485321 = 4520^2 + 3389^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31915721 is a prime.

It is a super-2 number, since 2×31915721² = 2037226493899682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (31915727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15957860 + 15957861.

It is an arithmetic number, because the mean of its divisors is an integer number (15957861).

Almost surely, 2^31915721 is an apocalyptic number.

It is an amenable number.

31915721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31915721 is an equidigital number, since it uses as much as digits as its factorization.

31915721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1890, while the sum is 29.

The square root of 31915721 is about 5649.4000566432. The cubic root of 31915721 is about 317.2012474859.

The spelling of 31915721 in words is "thirty-one million, nine hundred fifteen thousand, seven hundred twenty-one".