21518779617 has 6 divisors (see below), whose sum is σ = 31082681682. Its totient is φ = 14345853072.

The previous prime is 21518779589. The next prime is 21518779621. The reversal of 21518779617 is 71697781512.

21518779617 is a `hidden beast` number, since 2 + 1 + 5 + 18 + 7 + 7 + 9 + 617 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21317168016 + 201611601 = 146004^2 + 14199^2 .

It is not a de Polignac number, because 21518779617 - 2³² = 17223812321 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21518779627) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1195487748 + ... + 1195487765.

It is an arithmetic number, because the mean of its divisors is an integer number (5180446947).

Almost surely, 2^21518779617 is an apocalyptic number.

It is an amenable number.

21518779617 is a deficient number, since it is larger than the sum of its proper divisors (9563902065).

21518779617 is a wasteful number, since it uses less digits than its factorization.

21518779617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2390975519 (or 2390975516 counting only the distinct ones).

The product of its digits is 1481760, while the sum is 54.

The spelling of 21518779617 in words is "twenty-one billion, five hundred eighteen million, seven hundred seventy-nine thousand, six hundred seventeen".