21105972 has 18 divisors (see below), whose sum is σ = 53351298. Its totient is φ = 7035312.

The previous prime is 21105971. The next prime is 21105977. The reversal of 21105972 is 27950112.

It can be written as a sum of positive squares in only one way, i.e., 17089956 + 4016016 = 4134^2 + 2004^2 .

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105971) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 293103 + ... + 293174.

It is an arithmetic number, because the mean of its divisors is an integer number (2963961).

Almost surely, 2^21105972 is an apocalyptic number.

It is an amenable number.

21105972 is an abundant number, since it is smaller than the sum of its proper divisors (32245326).

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

21105972 is a wasteful number, since it uses less digits than its factorization.

21105972 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 586287 (or 586282 counting only the distinct ones).

The product of its (nonzero) digits is 1260, while the sum is 27.

The square root of 21105972 is about 4594.1236378661. The cubic root of 21105972 is about 276.3557165189.

The spelling of 21105972 in words is "twenty-one million, one hundred five thousand, nine hundred seventy-two".