21631621 has 4 divisors (see below), whose sum is σ = 23598144. Its totient is φ = 19665100.

The previous prime is 21631619. The next prime is 21631627. The reversal of 21631621 is 12613612.

21631621 is nontrivially palindromic in base 4.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21631621 - 2¹ = 21631619 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21631592 and 21631601.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21631627) 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, 983245 + ... + 983266.

It is an arithmetic number, because the mean of its divisors is an integer number (5899536).

Almost surely, 2^21631621 is an apocalyptic number.

It is an amenable number.

21631621 is a deficient number, since it is larger than the sum of its proper divisors (1966523).

21631621 is a wasteful number, since it uses less digits than its factorization.

21631621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1966522.

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

The square root of 21631621 is about 4650.9806492825. The cubic root of 21631621 is about 278.6311634587.

Subtracting from 21631621 its reverse (12613612), we obtain a square (9018009 = 3003²).

The spelling of 21631621 in words is "twenty-one million, six hundred thirty-one thousand, six hundred twenty-one".