644920085 has 4 divisors (see below), whose sum is σ = 773904108. Its totient is φ = 515936064.

The previous prime is 644920079. The next prime is 644920093. The reversal of 644920085 is 580029446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 580029446 = 2 ⋅290014723.

It can be written as a sum of positive squares in 2 ways, for example, as 508637809 + 136282276 = 22553^2 + 11674^2 .

It is a cyclic number.

It is not a de Polignac number, because 644920085 - 2¹² = 644915989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64492004 + ... + 64492013.

It is an arithmetic number, because the mean of its divisors is an integer number (193476027).

Almost surely, 2^644920085 is an apocalyptic number.

It is an amenable number.

644920085 is a deficient number, since it is larger than the sum of its proper divisors (128984023).

644920085 is a wasteful number, since it uses less digits than its factorization.

644920085 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128984022.

The product of its (nonzero) digits is 69120, while the sum is 38.

The square root of 644920085 is about 25395.2768246381. The cubic root of 644920085 is about 863.9765748143.

The spelling of 644920085 in words is "six hundred forty-four million, nine hundred twenty thousand, eighty-five".