21521631 has 4 divisors (see below), whose sum is σ = 28695512. Its totient is φ = 14347752.

The previous prime is 21521627. The next prime is 21521653. The reversal of 21521631 is 13612512.

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

It is not a de Polignac number, because 21521631 - 2² = 21521627 is a prime.

It is a super-2 number, since 2×21521631² = 926361201800322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21521598 and 21521607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521671) 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 in 3 ways as a sum of consecutive naturals, for example, 3586936 + ... + 3586941.

It is an arithmetic number, because the mean of its divisors is an integer number (7173878).

Almost surely, 2^21521631 is an apocalyptic number.

21521631 is a deficient number, since it is larger than the sum of its proper divisors (7173881).

21521631 is an equidigital number, since it uses as much as digits as its factorization.

21521631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7173880.

The product of its digits is 360, while the sum is 21.

The square root of 21521631 is about 4639.1411920742. The cubic root of 21521631 is about 278.1581101178.

The spelling of 21521631 in words is "twenty-one million, five hundred twenty-one thousand, six hundred thirty-one".