51720621665 has 16 divisors (see below), whose sum is σ = 63637586496. Its totient is φ = 40331860800.

The previous prime is 51720621629. The next prime is 51720621683. The reversal of 51720621665 is 56612602715.

It is not a de Polignac number, because 51720621665 - 2²⁰ = 51719573089 is a prime.

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, 139406 + ... + 350535.

It is an arithmetic number, because the mean of its divisors is an integer number (3977349156).

Almost surely, 2^51720621665 is an apocalyptic number.

It is an amenable number.

51720621665 is a deficient number, since it is larger than the sum of its proper divisors (11916964831).

51720621665 is a wasteful number, since it uses less digits than its factorization.

51720621665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 490480.

The product of its (nonzero) digits is 151200, while the sum is 41.

The spelling of 51720621665 in words is "fifty-one billion, seven hundred twenty million, six hundred twenty-one thousand, six hundred sixty-five".