644959986 has 16 divisors (see below), whose sum is σ = 1407185568. Its totient is φ = 195442400.

The previous prime is 644959961. The next prime is 644959999. The reversal of 644959986 is 689959446.

It is a super-2 number, since 2×644959986² = 831946767082240392, which contains 22 as substring.

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, 4885995 + ... + 4886126.

It is an arithmetic number, because the mean of its divisors is an integer number (87949098).

Almost surely, 2^644959986 is an apocalyptic number.

644959986 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

644959986 is an abundant number, since it is smaller than the sum of its proper divisors (762225582).

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

644959986 is a wasteful number, since it uses less digits than its factorization.

644959986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9772137.

The product of its digits is 16796160, while the sum is 60.

The square root of 644959986 is about 25396.0624113267. The cubic root of 644959986 is about 863.9943924319.

The spelling of 644959986 in words is "six hundred forty-four million, nine hundred fifty-nine thousand, nine hundred eighty-six".