640978957 has 2 divisors, whose sum is σ = 640978958. Its totient is φ = 640978956.

The previous prime is 640978937. The next prime is 640978963. The reversal of 640978957 is 759879046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 500461641 + 140517316 = 22371^2 + 11854^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640978957 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 640978898 and 640978907.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640978907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320489478 + 320489479.

It is an arithmetic number, because the mean of its divisors is an integer number (320489479).

Almost surely, 2^640978957 is an apocalyptic number.

It is an amenable number.

640978957 is a deficient number, since it is larger than the sum of its proper divisors (1).

640978957 is an equidigital number, since it uses as much as digits as its factorization.

640978957 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3810240, while the sum is 55.

The square root of 640978957 is about 25317.5622246693. The cubic root of 640978957 is about 862.2130477753.

The spelling of 640978957 in words is "six hundred forty million, nine hundred seventy-eight thousand, nine hundred fifty-seven".