21512654665 has 16 divisors (see below), whose sum is σ = 26232182928. Its totient is φ = 16934178816.

The previous prime is 21512654621. The next prime is 21512654687. The reversal of 21512654665 is 56645621512.

It can be written as a sum of positive squares in 8 ways, for example, as 1131380496 + 20381274169 = 33636^2 + 142763^2 .

It is a cyclic number.

It is not a de Polignac number, because 21512654665 - 2¹³ = 21512646473 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 44292 + ... + 212101.

It is an arithmetic number, because the mean of its divisors is an integer number (1639511433).

Almost surely, 2^21512654665 is an apocalyptic number.

It is an amenable number.

21512654665 is a deficient number, since it is larger than the sum of its proper divisors (4719528263).

21512654665 is a wasteful number, since it uses less digits than its factorization.

21512654665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 256668.

The product of its digits is 432000, while the sum is 43.

The spelling of 21512654665 in words is "twenty-one billion, five hundred twelve million, six hundred fifty-four thousand, six hundred sixty-five".