640749569 has 2 divisors, whose sum is σ = 640749570. Its totient is φ = 640749568.

The previous prime is 640749523. The next prime is 640749587. The reversal of 640749569 is 965947046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 640747969 + 1600 = 25313^2 + 40^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640749569 is a prime.

It is a super-2 number, since 2×640749569² = 821120020347371522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (640749589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320374784 + 320374785.

It is an arithmetic number, because the mean of its divisors is an integer number (320374785).

Almost surely, 2^640749569 is an apocalyptic number.

It is an amenable number.

640749569 is a deficient number, since it is larger than the sum of its proper divisors (1).

640749569 is an equidigital number, since it uses as much as digits as its factorization.

640749569 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1632960, while the sum is 50.

The square root of 640749569 is about 25313.0316042943. The cubic root of 640749569 is about 862.1101817230.

The spelling of 640749569 in words is "six hundred forty million, seven hundred forty-nine thousand, five hundred sixty-nine".