644863878 has 48 divisors (see below), whose sum is σ = 1425715200. Its totient is φ = 210603888.

The previous prime is 644863871. The next prime is 644863913. The reversal of 644863878 is 878368446.

644863878 is a `hidden beast` number, since 64 + 486 + 38 + 78 = 666.

It is a super-2 number, since 2×644863878² = 831698842298397768, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644863871) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 238651 + ... + 241337.

It is an arithmetic number, because the mean of its divisors is an integer number (29702400).

Almost surely, 2^644863878 is an apocalyptic number.

644863878 is an abundant number, since it is smaller than the sum of its proper divisors (780851322).

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

644863878 is a wasteful number, since it uses less digits than its factorization.

644863878 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2961 (or 2958 counting only the distinct ones).

The product of its digits is 6193152, while the sum is 54.

The square root of 644863878 is about 25394.1701577350. The cubic root of 644863878 is about 863.9514745766.

The spelling of 644863878 in words is "six hundred forty-four million, eight hundred sixty-three thousand, eight hundred seventy-eight".