21613031681 has 2 divisors, whose sum is σ = 21613031682. Its totient is φ = 21613031680.

The previous prime is 21613031599. The next prime is 21613031683. The reversal of 21613031681 is 18613031612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11159809600 + 10453222081 = 105640^2 + 102241^2 .

It is a cyclic number.

It is not a de Polignac number, because 21613031681 - 2¹⁸ = 21612769537 is a prime.

It is a super-2 number, since 2×21613031681² (a number of 21 digits) contains 22 as substring.

Together with 21613031683, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21613031683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10806515840 + 10806515841.

It is an arithmetic number, because the mean of its divisors is an integer number (10806515841).

Almost surely, 2^21613031681 is an apocalyptic number.

It is an amenable number.

21613031681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21613031681 is an equidigital number, since it uses as much as digits as its factorization.

21613031681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 32.

The spelling of 21613031681 in words is "twenty-one billion, six hundred thirteen million, thirty-one thousand, six hundred eighty-one".