31609778521 has 2 divisors, whose sum is σ = 31609778522. Its totient is φ = 31609778520.

The previous prime is 31609778491. The next prime is 31609778567. The reversal of 31609778521 is 12587790613.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17882375625 + 13727402896 = 133725^2 + 117164^2 .

It is an emirp because it is prime and its reverse (12587790613) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31609778521 - 2¹⁷ = 31609647449 is a prime.

It is not a weakly prime, because it can be changed into another prime (31609776521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15804889260 + 15804889261.

It is an arithmetic number, because the mean of its divisors is an integer number (15804889261).

Almost surely, 2^31609778521 is an apocalyptic number.

It is an amenable number.

31609778521 is a deficient number, since it is larger than the sum of its proper divisors (1).

31609778521 is an equidigital number, since it uses as much as digits as its factorization.

31609778521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 635040, while the sum is 49.

The spelling of 31609778521 in words is "thirty-one billion, six hundred nine million, seven hundred seventy-eight thousand, five hundred twenty-one".