31608721 has 2 divisors, whose sum is σ = 31608722. Its totient is φ = 31608720.

The previous prime is 31608713. The next prime is 31608727. The reversal of 31608721 is 12780613.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 27447121 + 4161600 = 5239^2 + 2040^2 .

It is an emirp because it is prime and its reverse (12780613) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31608721 - 2³ = 31608713 is a prime.

It is a super-2 number, since 2×31608721² = 1998222486511682, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 31608721.

It is not a weakly prime, because it can be changed into another prime (31608727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15804360 + 15804361.

It is an arithmetic number, because the mean of its divisors is an integer number (15804361).

Almost surely, 2^31608721 is an apocalyptic number.

It is an amenable number.

31608721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31608721 is an equidigital number, since it uses as much as digits as its factorization.

31608721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 31608721 is about 5622.1633736490. The cubic root of 31608721 is about 316.1809070680.

It can be divided in two parts, 3160 and 8721, that added together give a square (11881 = 109²).

The spelling of 31608721 in words is "thirty-one million, six hundred eight thousand, seven hundred twenty-one".