640715861 has 2 divisors, whose sum is σ = 640715862. Its totient is φ = 640715860.

The previous prime is 640715851. The next prime is 640715863. The reversal of 640715861 is 168517046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 632271025 + 8444836 = 25145^2 + 2906^2 .

It is a cyclic number.

It is not a de Polignac number, because 640715861 - 2¹⁸ = 640453717 is a prime.

Together with 640715863, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640715863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320357930 + 320357931.

It is an arithmetic number, because the mean of its divisors is an integer number (320357931).

Almost surely, 2^640715861 is an apocalyptic number.

It is an amenable number.

640715861 is a deficient number, since it is larger than the sum of its proper divisors (1).

640715861 is an equidigital number, since it uses as much as digits as its factorization.

640715861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40320, while the sum is 38.

The square root of 640715861 is about 25312.3657724836. The cubic root of 640715861 is about 862.0950637419.

The spelling of 640715861 in words is "six hundred forty million, seven hundred fifteen thousand, eight hundred sixty-one".