644504557 has 4 divisors (see below), whose sum is σ = 654124096. Its totient is φ = 634885020.

The previous prime is 644504519. The next prime is 644504563. The reversal of 644504557 is 755405446.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 755405446 = 2 ⋅377702723.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644504557 is a prime.

It is a super-2 number, since 2×644504557² = 830772247987532498, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644504057) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4809669 + ... + 4809802.

It is an arithmetic number, because the mean of its divisors is an integer number (163531024).

Almost surely, 2^644504557 is an apocalyptic number.

644504557 is a gapful number since it is divisible by the number (67) formed by its first and last digit.

It is an amenable number.

644504557 is a deficient number, since it is larger than the sum of its proper divisors (9619539).

644504557 is an equidigital number, since it uses as much as digits as its factorization.

644504557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9619538.

The product of its (nonzero) digits is 336000, while the sum is 40.

The square root of 644504557 is about 25387.0943000573. The cubic root of 644504557 is about 863.7909789046.

The spelling of 644504557 in words is "six hundred forty-four million, five hundred four thousand, five hundred fifty-seven".