644774487761 has 2 divisors, whose sum is σ = 644774487762. Its totient is φ = 644774487760.

The previous prime is 644774487737. The next prime is 644774487787. The reversal of 644774487761 is 167784477446.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 529065662161 + 115708825600 = 727369^2 + 340160^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644774487761 is a prime.

It is not a weakly prime, because it can be changed into another prime (644774487701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322387243880 + 322387243881.

It is an arithmetic number, because the mean of its divisors is an integer number (322387243881).

Almost surely, 2^644774487761 is an apocalyptic number.

It is an amenable number.

644774487761 is a deficient number, since it is larger than the sum of its proper divisors (1).

644774487761 is an equidigital number, since it uses as much as digits as its factorization.

644774487761 is an evil number, because the sum of its binary digits is even.

The product of its digits is 177020928, while the sum is 65.

The spelling of 644774487761 in words is "six hundred forty-four billion, seven hundred seventy-four million, four hundred eighty-seven thousand, seven hundred sixty-one".