644340761 has 2 divisors, whose sum is σ = 644340762. Its totient is φ = 644340760.

The previous prime is 644340737. The next prime is 644340841. The reversal of 644340761 is 167043446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 611622361 + 32718400 = 24731^2 + 5720^2 .

It is a cyclic number.

It is not a de Polignac number, because 644340761 - 2¹⁴ = 644324377 is a prime.

It is not a weakly prime, because it can be changed into another prime (644340701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322170380 + 322170381.

It is an arithmetic number, because the mean of its divisors is an integer number (322170381).

Almost surely, 2^644340761 is an apocalyptic number.

It is an amenable number.

644340761 is a deficient number, since it is larger than the sum of its proper divisors (1).

644340761 is an equidigital number, since it uses as much as digits as its factorization.

644340761 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48384, while the sum is 35.

The square root of 644340761 is about 25383.8681252484. The cubic root of 644340761 is about 863.7177973715.

The spelling of 644340761 in words is "six hundred forty-four million, three hundred forty thousand, seven hundred sixty-one".