51720021999 has 48 divisors (see below), whose sum is σ = 79039717120. Its totient is φ = 32589445392.

The previous prime is 51720021967. The next prime is 51720022019. The reversal of 51720021999 is 99912002715.

51720021999 is a `hidden beast` number, since 517 + 20 + 0 + 21 + 9 + 99 = 666.

It is not a de Polignac number, because 51720021999 - 2⁵ = 51720021967 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51720022999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 39692382 + ... + 39693684.

Almost surely, 2^51720021999 is an apocalyptic number.

51720021999 is a deficient number, since it is larger than the sum of its proper divisors (27319695121).

51720021999 is a wasteful number, since it uses less digits than its factorization.

51720021999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2009 (or 1968 counting only the distinct ones).

The product of its (nonzero) digits is 102060, while the sum is 45.

The spelling of 51720021999 in words is "fifty-one billion, seven hundred twenty million, twenty-one thousand, nine hundred ninety-nine".