21663444 has 24 divisors (see below), whose sum is σ = 55143648. Its totient is φ = 6564640.

The previous prime is 21663437. The next prime is 21663497. The reversal of 21663444 is 44436612.

It is a super-2 number, since 2×21663444² = 938609611882272, which contains 22 as substring.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 81927 + ... + 82190.

It is an arithmetic number, because the mean of its divisors is an integer number (2297652).

Almost surely, 2^21663444 is an apocalyptic number.

It is an amenable number.

21663444 is an abundant number, since it is smaller than the sum of its proper divisors (33480204).

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

21663444 is a wasteful number, since it uses less digits than its factorization.

21663444 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 164135 (or 164133 counting only the distinct ones).

The product of its digits is 13824, while the sum is 30.

The square root of 21663444 is about 4654.4004984530. The cubic root of 21663444 is about 278.7677310472.

The spelling of 21663444 in words is "twenty-one million, six hundred sixty-three thousand, four hundred forty-four".