640975681 has 2 divisors, whose sum is σ = 640975682. Its totient is φ = 640975680.

The previous prime is 640975651. The next prime is 640975703. The reversal of 640975681 is 186579046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 619213456 + 21762225 = 24884^2 + 4665^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640975681 is a prime.

It is a super-2 number, since 2×640975681² = 821699647266827522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (640975651) 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, 320487840 + 320487841.

It is an arithmetic number, because the mean of its divisors is an integer number (320487841).

Almost surely, 2^640975681 is an apocalyptic number.

It is an amenable number.

640975681 is a deficient number, since it is larger than the sum of its proper divisors (1).

640975681 is an equidigital number, since it uses as much as digits as its factorization.

640975681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 362880, while the sum is 46.

The square root of 640975681 is about 25317.4975264144. The cubic root of 640975681 is about 862.2115788687.

The spelling of 640975681 in words is "six hundred forty million, nine hundred seventy-five thousand, six hundred eighty-one".