656881721 has 4 divisors (see below), whose sum is σ = 658643172. Its totient is φ = 655120272.

The previous prime is 656881711. The next prime is 656881741. The reversal of 656881721 is 127188656.

It is a happy number.

656881721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 516198400 + 140683321 = 22720^2 + 11861^2 .

It is a cyclic number.

It is not a de Polignac number, because 656881721 - 2⁶ = 656881657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (656881711) 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, 880166 + ... + 880911.

It is an arithmetic number, because the mean of its divisors is an integer number (164660793).

Almost surely, 2^656881721 is an apocalyptic number.

It is an amenable number.

656881721 is a deficient number, since it is larger than the sum of its proper divisors (1761451).

656881721 is a wasteful number, since it uses less digits than its factorization.

656881721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1761450.

The product of its digits is 161280, while the sum is 44.

The square root of 656881721 is about 25629.7038804587. The cubic root of 656881721 is about 869.2854135777.

The spelling of 656881721 in words is "six hundred fifty-six million, eight hundred eighty-one thousand, seven hundred twenty-one".