644021905 has 8 divisors (see below), whose sum is σ = 772964712. Its totient is φ = 515125248.

The previous prime is 644021899. The next prime is 644021923. The reversal of 644021905 is 509120446.

It can be written as a sum of positive squares in 4 ways, for example, as 93837969 + 550183936 = 9687^2 + 23456^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644021905 - 2⁹ = 644021393 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40567 + ... + 54163.

It is an arithmetic number, because the mean of its divisors is an integer number (96620589).

Almost surely, 2^644021905 is an apocalyptic number.

It is an amenable number.

644021905 is a deficient number, since it is larger than the sum of its proper divisors (128942807).

644021905 is a wasteful number, since it uses less digits than its factorization.

644021905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23075.

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 644021905 is about 25377.5866661903. The cubic root of 644021905 is about 863.5753018375.

The spelling of 644021905 in words is "six hundred forty-four million, twenty-one thousand, nine hundred five".