644641655 has 16 divisors (see below), whose sum is σ = 886019904. Its totient is φ = 441070080.

The previous prime is 644641643. The next prime is 644641687. The reversal of 644641655 is 556146446.

It is not a de Polignac number, because 644641655 - 2¹⁰ = 644640631 is a prime.

It is a super-2 number, since 2×644641655² = 831125726722278050, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3842 + ... + 36111.

It is an arithmetic number, because the mean of its divisors is an integer number (55376244).

Almost surely, 2^644641655 is an apocalyptic number.

644641655 is a deficient number, since it is larger than the sum of its proper divisors (241378249).

644641655 is a wasteful number, since it uses less digits than its factorization.

644641655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40426.

The product of its digits is 345600, while the sum is 41.

The square root of 644641655 is about 25389.7943079498. The cubic root of 644641655 is about 863.8522226503.

The spelling of 644641655 in words is "six hundred forty-four million, six hundred forty-one thousand, six hundred fifty-five".