644669761 has 4 divisors (see below), whose sum is σ = 645211332. Its totient is φ = 644128192.

The previous prime is 644669747. The next prime is 644669771. The reversal of 644669761 is 167966446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 167966446 = 2 ⋅83983223.

It can be written as a sum of positive squares in 2 ways, for example, as 192682161 + 451987600 = 13881^2 + 21260^2 .

It is a cyclic number.

It is not a de Polignac number, because 644669761 - 2¹⁹ = 644145473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644669741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 268996 + ... + 271381.

It is an arithmetic number, because the mean of its divisors is an integer number (161302833).

Almost surely, 2^644669761 is an apocalyptic number.

It is an amenable number.

644669761 is a deficient number, since it is larger than the sum of its proper divisors (541571).

644669761 is a wasteful number, since it uses less digits than its factorization.

644669761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 541570.

The product of its digits is 1306368, while the sum is 49.

The square root of 644669761 is about 25390.3477920252. The cubic root of 644669761 is about 863.8647769522.

The spelling of 644669761 in words is "six hundred forty-four million, six hundred sixty-nine thousand, seven hundred sixty-one".