21397644 has 18 divisors (see below), whose sum is σ = 54088580. Its totient is φ = 7132536.

The previous prime is 21397633. The next prime is 21397669. The reversal of 21397644 is 44679312.

21397644 is a `hidden beast` number, since 2 + 1 + 3 + 9 + 7 + 644 = 666.

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 594379 = 21397644 / (2 + 1 + 3 + 9 + 7 + 6 + 4 + 4).

It is a junction number, because it is equal to n+sod(n) for n = 21397599 and 21397608.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 297154 + ... + 297225.

Almost surely, 2^21397644 is an apocalyptic number.

It is an amenable number.

21397644 is an abundant number, since it is smaller than the sum of its proper divisors (32690936).

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

21397644 is a wasteful number, since it uses less digits than its factorization.

21397644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 594389 (or 594384 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21397644 is about 4625.7587485730. The cubic root of 21397644 is about 277.6229209509.

The spelling of 21397644 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred forty-four".