644733520209 has 81 divisors (see below), whose sum is σ = 1013275898089. Its totient is φ = 410180510520.

The previous prime is 644733520177. The next prime is 644733520229. The reversal of 644733520209 is 902025337446.

The square root of 644733520209 is 802953.

It is a perfect power (a square), and thus also a powerful number.

644733520209 is a `hidden beast` number, since 64 + 47 + 3 + 3 + 520 + 20 + 9 = 666.

It is a tau number, because it is divible by the number of its divisors (81).

It is not a de Polignac number, because 644733520209 - 2⁵ = 644733520177 is a prime.

It is a super-2 number, since 2×644733520209² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644733520229) by changing a digit.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 1495901224 + ... + 1495901654.

Almost surely, 2^644733520209 is an apocalyptic number.

644733520209 is a gapful number since it is divisible by the number (69) formed by its first and last digit.

644733520209 is the 802953-rd square number.

644733520209 is the 401477-th centered octagonal number.

It is an amenable number.

644733520209 is a deficient number, since it is larger than the sum of its proper divisors (368542377880).

644733520209 is an frugal number, since it uses more digits than its factorization.

644733520209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 932 (or 457 counting only the distinct ones).

The product of its (nonzero) digits is 1088640, while the sum is 45.

The spelling of 644733520209 in words is "six hundred forty-four billion, seven hundred thirty-three million, five hundred twenty thousand, two hundred nine".