21615631 has 4 divisors (see below), whose sum is σ = 21629752. Its totient is φ = 21601512.

The previous prime is 21615617. The next prime is 21615637. The reversal of 21615631 is 13651612.

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 21615631 - 2⁵ = 21615599 is a prime.

It is a super-2 number, since 2×21615631² = 934471007056322, 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 = 21615596 and 21615605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21615637) 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, 4440 + ... + 7933.

It is an arithmetic number, because the mean of its divisors is an integer number (5407438).

Almost surely, 2^21615631 is an apocalyptic number.

21615631 is a deficient number, since it is larger than the sum of its proper divisors (14121).

21615631 is a wasteful number, since it uses less digits than its factorization.

21615631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14120.

The product of its digits is 1080, while the sum is 25.

The square root of 21615631 is about 4649.2613391807. The cubic root of 21615631 is about 278.5624922214.

The spelling of 21615631 in words is "twenty-one million, six hundred fifteen thousand, six hundred thirty-one".