20721557686516 has 12 divisors (see below), whose sum is σ = 36273859755588. Its totient is φ = 10357597756352.

The previous prime is 20721557686513. The next prime is 20721557686547. The reversal of 20721557686516 is 61568675512702.

It can be written as a sum of positive squares in 2 ways, for example, as 11030502288400 + 9691055398116 = 3321220^2 + 3113046^2 .

It is a super-2 number, since 2×20721557686516² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721557686513) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 795257071 + ... + 795283126.

It is an arithmetic number, because the mean of its divisors is an integer number (3022821646299).

Almost surely, 2^{20721557686516} is an apocalyptic number.

It is an amenable number.

20721557686516 is a deficient number, since it is larger than the sum of its proper divisors (15552302069072).

20721557686516 is a wasteful number, since it uses less digits than its factorization.

20721557686516 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1590543458 (or 1590543456 counting only the distinct ones).

The product of its (nonzero) digits is 42336000, while the sum is 61.

The spelling of 20721557686516 in words is "twenty trillion, seven hundred twenty-one billion, five hundred fifty-seven million, six hundred eighty-six thousand, five hundred sixteen".