21621631 has 2 divisors, whose sum is σ = 21621632. Its totient is φ = 21621630.

The previous prime is 21621629. The next prime is 21621641. The reversal of 21621631 is 13612612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21621631 - 2¹ = 21621629 is a prime.

It is a super-2 number, since 2×21621631² = 934989854200322, which contains 22 as substring.

Together with 21621629, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21621641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810815 + 10810816.

It is an arithmetic number, because the mean of its divisors is an integer number (10810816).

Almost surely, 2^21621631 is an apocalyptic number.

21621631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621631 is an equidigital number, since it uses as much as digits as its factorization.

21621631 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 432, while the sum is 22.

The square root of 21621631 is about 4649.9065582009. The cubic root of 21621631 is about 278.5882640087.

The spelling of 21621631 in words is "twenty-one million, six hundred twenty-one thousand, six hundred thirty-one".