21565437 has 16 divisors (see below), whose sum is σ = 30375360. Its totient is φ = 13571712.

The previous prime is 21565417. The next prime is 21565447. The reversal of 21565437 is 73456512.

It is not a de Polignac number, because 21565437 - 2¹² = 21561341 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21565398 and 21565407.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565417) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22153 + ... + 23105.

It is an arithmetic number, because the mean of its divisors is an integer number (1898460).

Almost surely, 2^21565437 is an apocalyptic number.

It is an amenable number.

21565437 is a deficient number, since it is larger than the sum of its proper divisors (8809923).

21565437 is a wasteful number, since it uses less digits than its factorization.

21565437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1372.

The product of its digits is 25200, while the sum is 33.

The square root of 21565437 is about 4643.8601400128. The cubic root of 21565437 is about 278.3467069801.

The spelling of 21565437 in words is "twenty-one million, five hundred sixty-five thousand, four hundred thirty-seven".