644087761 has 2 divisors, whose sum is σ = 644087762. Its totient is φ = 644087760.

The previous prime is 644087723. The next prime is 644087803. The reversal of 644087761 is 167780446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 643890625 + 197136 = 25375^2 + 444^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644087761 is a prime.

It is not a weakly prime, because it can be changed into another prime (644087701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322043880 + 322043881.

It is an arithmetic number, because the mean of its divisors is an integer number (322043881).

Almost surely, 2^644087761 is an apocalyptic number.

It is an amenable number.

644087761 is a deficient number, since it is larger than the sum of its proper divisors (1).

644087761 is an equidigital number, since it uses as much as digits as its factorization.

644087761 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 225792, while the sum is 43.

The square root of 644087761 is about 25378.8841559277. The cubic root of 644087761 is about 863.6047364867.

The spelling of 644087761 in words is "six hundred forty-four million, eighty-seven thousand, seven hundred sixty-one".