21657631 has 2 divisors, whose sum is σ = 21657632. Its totient is φ = 21657630.

The previous prime is 21657611. The next prime is 21657637. The reversal of 21657631 is 13675612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21657631 - 2⁵ = 21657599 is a prime.

It is a super-2 number, since 2×21657631² = 938105961064322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21657593 and 21657602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21657637) 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, 10828815 + 10828816.

It is an arithmetic number, because the mean of its divisors is an integer number (10828816).

Almost surely, 2^21657631 is an apocalyptic number.

21657631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21657631 is an equidigital number, since it uses as much as digits as its factorization.

21657631 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7560, while the sum is 31.

The square root of 21657631 is about 4653.7759937496. The cubic root of 21657631 is about 278.7427946953.

The spelling of 21657631 in words is "twenty-one million, six hundred fifty-seven thousand, six hundred thirty-one".