21165631 has 4 divisors (see below), whose sum is σ = 21199192. Its totient is φ = 21132072.

The previous prime is 21165623. The next prime is 21165667. The reversal of 21165631 is 13656112.

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 21165631 - 2³ = 21165623 is a prime.

It is a super-2 number, since 2×21165631² = 895967871256322, 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 = 21165596 and 21165605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21165671) 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, 15816 + ... + 17101.

It is an arithmetic number, because the mean of its divisors is an integer number (5299798).

Almost surely, 2^21165631 is an apocalyptic number.

21165631 is a deficient number, since it is larger than the sum of its proper divisors (33561).

21165631 is an equidigital number, since it uses as much as digits as its factorization.

21165631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33560.

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

The square root of 21165631 is about 4600.6120245028. The cubic root of 21165631 is about 276.6158576718.

The spelling of 21165631 in words is "twenty-one million, one hundred sixty-five thousand, six hundred thirty-one".