21623644 has 12 divisors (see below), whose sum is σ = 43247344. Its totient is φ = 9267264.

The previous prime is 21623639. The next prime is 21623663. The reversal of 21623644 is 44632612.

21623644 is an admirable number.

It is a Harshad number since it is a multiple of its sum of digits (28), and also a Moran number because the ratio is a prime number: 772273 = 21623644 / (2 + 1 + 6 + 2 + 3 + 6 + 4 + 4).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 386109 + ... + 386164.

Almost surely, 2^21623644 is an apocalyptic number.

It is an amenable number.

21623644 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21623644 is a wasteful number, since it uses less digits than its factorization.

21623644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 772284 (or 772282 counting only the distinct ones).

The product of its digits is 6912, while the sum is 28.

The square root of 21623644 is about 4650.1230091257. The cubic root of 21623644 is about 278.5969093752.

The spelling of 21623644 in words is "twenty-one million, six hundred twenty-three thousand, six hundred forty-four".