51515625721 has 16 divisors (see below), whose sum is σ = 60187405824. Its totient is φ = 43173814464.

The previous prime is 51515625697. The next prime is 51515625739. The reversal of 51515625721 is 12752651515.

It is a cyclic number.

It is not a de Polignac number, because 51515625721 - 2⁹ = 51515625209 is a prime.

It is not an unprimeable number, because it can be changed into a prime (51515625751) 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, 255991 + ... + 410563.

It is an arithmetic number, because the mean of its divisors is an integer number (3761712864).

Almost surely, 2^51515625721 is an apocalyptic number.

It is an amenable number.

51515625721 is a deficient number, since it is larger than the sum of its proper divisors (8671780103).

51515625721 is a wasteful number, since it uses less digits than its factorization.

51515625721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 155640.

The product of its digits is 105000, while the sum is 40.

The spelling of 51515625721 in words is "fifty-one billion, five hundred fifteen million, six hundred twenty-five thousand, seven hundred twenty-one".