21390944 has 24 divisors (see below), whose sum is σ = 42243768. Its totient is φ = 10662400.

The previous prime is 21390911. The next prime is 21390977. The reversal of 21390944 is 44909312.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21390911) and next prime (21390977).

It is a super-2 number, since 2×21390944² = 915144970422272, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a self number, because there is not a number n which added to its sum of digits gives 21390944.

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, 11999 + ... + 13665.

It is an arithmetic number, because the mean of its divisors is an integer number (1760157).

Almost surely, 2^21390944 is an apocalyptic number.

It is an amenable number.

21390944 is a deficient number, since it is larger than the sum of its proper divisors (20852824).

21390944 is a wasteful number, since it uses less digits than its factorization.

21390944 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2078 (or 2070 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 32.

The square root of 21390944 is about 4625.0344863579. The cubic root of 21390944 is about 277.5939416274.

The spelling of 21390944 in words is "twenty-one million, three hundred ninety thousand, nine hundred forty-four".