21665724621 has 32 divisors (see below), whose sum is σ = 31145306112. Its totient is φ = 13364070720.

The previous prime is 21665724611. The next prime is 21665724649. The reversal of 21665724621 is 12642756612.

It is not a de Polignac number, because 21665724621 - 2⁹ = 21665724109 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665724611) 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, 217926 + ... + 301368.

It is an arithmetic number, because the mean of its divisors is an integer number (973290816).

Almost surely, 2^21665724621 is an apocalyptic number.

It is an amenable number.

21665724621 is a deficient number, since it is larger than the sum of its proper divisors (9479581491).

21665724621 is a wasteful number, since it uses less digits than its factorization.

21665724621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83593.

The product of its digits is 241920, while the sum is 42.

The spelling of 21665724621 in words is "twenty-one billion, six hundred sixty-five million, seven hundred twenty-four thousand, six hundred twenty-one".