644670261 has 12 divisors (see below), whose sum is σ = 963300780. Its totient is φ = 414960000.

The previous prime is 644670253. The next prime is 644670269. The reversal of 644670261 is 162076446.

644670261 is a `hidden beast` number, since 644 + 6 + 7 + 0 + 2 + 6 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (644670253) and next prime (644670269).

It can be written as a sum of positive squares in 2 ways, for example, as 301716900 + 342953361 = 17370^2 + 18519^2 .

It is not a de Polignac number, because 644670261 - 2³ = 644670253 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644670269) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1234740 + ... + 1235261.

It is an arithmetic number, because the mean of its divisors is an integer number (80275065).

Almost surely, 2^644670261 is an apocalyptic number.

It is an amenable number.

644670261 is a deficient number, since it is larger than the sum of its proper divisors (318630519).

644670261 is a wasteful number, since it uses less digits than its factorization.

644670261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2470036 (or 2470033 counting only the distinct ones).

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

The square root of 644670261 is about 25390.3576382847. The cubic root of 644670261 is about 863.8650002873.

The spelling of 644670261 in words is "six hundred forty-four million, six hundred seventy thousand, two hundred sixty-one".