21371631 has 4 divisors (see below), whose sum is σ = 28495512. Its totient is φ = 14247752.

The previous prime is 21371627. The next prime is 21371653. The reversal of 21371631 is 13617312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21371631 - 2² = 21371627 is a prime.

It is a super-2 number, since 2×21371631² = 913493223200322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21375631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3561936 + ... + 3561941.

It is an arithmetic number, because the mean of its divisors is an integer number (7123878).

Almost surely, 2^21371631 is an apocalyptic number.

21371631 is a deficient number, since it is larger than the sum of its proper divisors (7123881).

21371631 is an equidigital number, since it uses as much as digits as its factorization.

21371631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7123880.

The product of its digits is 756, while the sum is 24.

The square root of 21371631 is about 4622.9461385571. The cubic root of 21371631 is about 277.5103737701.

Adding to 21371631 its reverse (13617312), we get a palindrome (34988943).

The spelling of 21371631 in words is "twenty-one million, three hundred seventy-one thousand, six hundred thirty-one".