21565641 has 16 divisors (see below), whose sum is σ = 29300544. Its totient is φ = 14106624.

The previous prime is 21565633. The next prime is 21565667. The reversal of 21565641 is 14656512.

It is not a de Polignac number, because 21565641 - 2³ = 21565633 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21565599 and 21565608.

It is not an unprimeable number, because it can be changed into a prime (21565601) 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, 63825 + ... + 64161.

It is an arithmetic number, because the mean of its divisors is an integer number (1831284).

Almost surely, 2^21565641 is an apocalyptic number.

It is an amenable number.

21565641 is a deficient number, since it is larger than the sum of its proper divisors (7734903).

21565641 is a wasteful number, since it uses less digits than its factorization.

21565641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 680.

The product of its digits is 7200, while the sum is 30.

The square root of 21565641 is about 4643.8821044467. The cubic root of 21565641 is about 278.3475846584.

It can be divided in two parts, 215 and 65641, that added together give a palindrome (65856).

The spelling of 21565641 in words is "twenty-one million, five hundred sixty-five thousand, six hundred forty-one".