644051556 has 18 divisors (see below), whose sum is σ = 1628019302. Its totient is φ = 214683840.

The previous prime is 644051539. The next prime is 644051557. The reversal of 644051556 is 655150446.

644051556 is a `hidden beast` number, since 64 + 40 + 5 + 1 + 556 = 666.

It can be written as a sum of positive squares in only one way, i.e., 331822656 + 312228900 = 18216^2 + 17670^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a super-2 number, since 2×644051556² = 829604813572042272, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 17890321 = 644051556 / (6 + 4 + 4 + 0 + 5 + 1 + 5 + 5 + 6).

It is a self number, because there is not a number n which added to its sum of digits gives 644051556.

It is not an unprimeable number, because it can be changed into a prime (644051557) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8945125 + ... + 8945196.

Almost surely, 2^644051556 is an apocalyptic number.

It is an amenable number.

644051556 is an abundant number, since it is smaller than the sum of its proper divisors (983967746).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644051556 is a wasteful number, since it uses less digits than its factorization.

644051556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17890331 (or 17890326 counting only the distinct ones).

The product of its (nonzero) digits is 72000, while the sum is 36.

The square root of 644051556 is about 25378.1708560724. The cubic root of 644051556 is about 863.5885547398.

The spelling of 644051556 in words is "six hundred forty-four million, fifty-one thousand, five hundred fifty-six".