31172515721 has 2 divisors, whose sum is σ = 31172515722. Its totient is φ = 31172515720.

The previous prime is 31172515711. The next prime is 31172515727. The reversal of 31172515721 is 12751527113.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 24527005321 + 6645510400 = 156611^2 + 81520^2 .

It is a cyclic number.

It is not a de Polignac number, because 31172515721 - 2³⁰ = 30098773897 is a prime.

It is not a weakly prime, because it can be changed into another prime (31172515727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15586257860 + 15586257861.

It is an arithmetic number, because the mean of its divisors is an integer number (15586257861).

Almost surely, 2^31172515721 is an apocalyptic number.

It is an amenable number.

31172515721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31172515721 is an equidigital number, since it uses as much as digits as its factorization.

31172515721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14700, while the sum is 35.

The spelling of 31172515721 in words is "thirty-one billion, one hundred seventy-two million, five hundred fifteen thousand, seven hundred twenty-one".