21631599721 has 2 divisors, whose sum is σ = 21631599722. Its totient is φ = 21631599720.

The previous prime is 21631599707. The next prime is 21631599727. The reversal of 21631599721 is 12799513612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21100758121 + 530841600 = 145261^2 + 23040^2 .

It is a cyclic number.

It is not a de Polignac number, because 21631599721 - 2⁷ = 21631599593 is a prime.

It is a super-2 number, since 2×21631599721² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21631599727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815799860 + 10815799861.

It is an arithmetic number, because the mean of its divisors is an integer number (10815799861).

Almost surely, 2^21631599721 is an apocalyptic number.

It is an amenable number.

21631599721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21631599721 is an equidigital number, since it uses as much as digits as its factorization.

21631599721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 204120, while the sum is 46.

The spelling of 21631599721 in words is "twenty-one billion, six hundred thirty-one million, five hundred ninety-nine thousand, seven hundred twenty-one".