656978721 has 12 divisors (see below), whose sum is σ = 1018987632. Its totient is φ = 375416328.

The previous prime is 656978671. The next prime is 656978741. The reversal of 656978721 is 127879656.

It is not a de Polignac number, because 656978721 - 2¹¹ = 656976673 is a prime.

It is not an unprimeable number, because it can be changed into a prime (656978741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2234475 + ... + 2234768.

It is an arithmetic number, because the mean of its divisors is an integer number (84915636).

Almost surely, 2^656978721 is an apocalyptic number.

It is an amenable number.

656978721 is a deficient number, since it is larger than the sum of its proper divisors (362008911).

656978721 is a wasteful number, since it uses less digits than its factorization.

656978721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4469260 (or 4469253 counting only the distinct ones).

The product of its digits is 1270080, while the sum is 51.

The square root of 656978721 is about 25631.5961461630. The cubic root of 656978721 is about 869.3281998370.

The spelling of 656978721 in words is "six hundred fifty-six million, nine hundred seventy-eight thousand, seven hundred twenty-one".