21720516772 has 12 divisors (see below), whose sum is σ = 38020432716. Its totient is φ = 10857536000.

The previous prime is 21720516749. The next prime is 21720516793. The reversal of 21720516772 is 27761502712.

It can be written as a sum of positive squares in 2 ways, for example, as 11779629156 + 9940887616 = 108534^2 + 99704^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 662593 + ... + 694600.

It is an arithmetic number, because the mean of its divisors is an integer number (3168369393).

Almost surely, 2^21720516772 is an apocalyptic number.

It is an amenable number.

21720516772 is a deficient number, since it is larger than the sum of its proper divisors (16299915944).

21720516772 is a wasteful number, since it uses less digits than its factorization.

21720516772 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1361198 (or 1361196 counting only the distinct ones).

The product of its (nonzero) digits is 82320, while the sum is 40.

The spelling of 21720516772 in words is "twenty-one billion, seven hundred twenty million, five hundred sixteen thousand, seven hundred seventy-two".