644207661 has 20 divisors (see below), whose sum is σ = 963531712. Its totient is φ = 428937768.

The previous prime is 644207657. The next prime is 644207671. The reversal of 644207661 is 166702446.

644207661 is a `hidden beast` number, since 644 + 2 + 0 + 7 + 6 + 6 + 1 = 666.

644207661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 644207661 - 2² = 644207657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644207611) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 67020 + ... + 76026.

Almost surely, 2^644207661 is an apocalyptic number.

It is an amenable number.

644207661 is a deficient number, since it is larger than the sum of its proper divisors (319324051).

644207661 is an equidigital number, since it uses as much as digits as its factorization.

644207661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9902 (or 9893 counting only the distinct ones).

The product of its (nonzero) digits is 48384, while the sum is 36.

The square root of 644207661 is about 25381.2462459982. The cubic root of 644207661 is about 863.6583212048.

The spelling of 644207661 in words is "six hundred forty-four million, two hundred seven thousand, six hundred sixty-one".