21565973 has 32 divisors (see below), whose sum is σ = 27095040. Its totient is φ = 16885440.

The previous prime is 21565967. The next prime is 21565993. The reversal of 21565973 is 37956512.

It is a happy number.

It is not a de Polignac number, because 21565973 - 2²⁴ = 4788757 is a prime.

It is a Smith number, since the sum of its digits (38) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565933) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 259790 + ... + 259872.

It is an arithmetic number, because the mean of its divisors is an integer number (846720).

Almost surely, 2^21565973 is an apocalyptic number.

21565973 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

It is an amenable number.

21565973 is a deficient number, since it is larger than the sum of its proper divisors (5529067).

21565973 is a wasteful number, since it uses less digits than its factorization.

21565973 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 209.

The product of its digits is 56700, while the sum is 38.

The square root of 21565973 is about 4643.9178502639. The cubic root of 21565973 is about 278.3490130250.

The spelling of 21565973 in words is "twenty-one million, five hundred sixty-five thousand, nine hundred seventy-three".