656991 has 10 divisors (see below), whose sum is σ = 981552. Its totient is φ = 437940.

The previous prime is 656989. The next prime is 656993. The reversal of 656991 is 199656.

656991 is a `hidden beast` number, since 6 + 569 + 91 = 666.

656991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (656989) and next prime (656993).

It is not a de Polignac number, because 656991 - 2¹ = 656989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (656993) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 3975 + ... + 4136.

2⁶⁵⁶⁹⁹¹ is an apocalyptic number.

656991 is a deficient number, since it is larger than the sum of its proper divisors (324561).

656991 is an equidigital number, since it uses as much as digits as its factorization.

656991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8123 (or 8114 counting only the distinct ones).

The product of its digits is 14580, while the sum is 36.

The square root of 656991 is about 810.5498133983. The cubic root of 656991 is about 86.9333615748.

Subtracting from 656991 its product of digits (14580), we obtain a triangular number (642411 = T₁₁₃₃).

It can be divided in two parts, 65 and 6991, that added together give a square (7056 = 84²).

The spelling of 656991 in words is "six hundred fifty-six thousand, nine hundred ninety-one".