31690721 has 2 divisors, whose sum is σ = 31690722. Its totient is φ = 31690720.

The previous prime is 31690717. The next prime is 31690733. The reversal of 31690721 is 12709613.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 27447121 + 4243600 = 5239^2 + 2060^2 .

It is a cyclic number.

It is not a de Polignac number, because 31690721 - 2² = 31690717 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (31690741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15845360 + 15845361.

It is an arithmetic number, because the mean of its divisors is an integer number (15845361).

Almost surely, 2^31690721 is an apocalyptic number.

It is an amenable number.

31690721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31690721 is an equidigital number, since it uses as much as digits as its factorization.

31690721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268, while the sum is 29.

The square root of 31690721 is about 5629.4512165930. The cubic root of 31690721 is about 316.4540853327.

The spelling of 31690721 in words is "thirty-one million, six hundred ninety thousand, seven hundred twenty-one".