644806261 has 4 divisors (see below), whose sum is σ = 703425024. Its totient is φ = 586187500.

The previous prime is 644806247. The next prime is 644806307. The reversal of 644806261 is 162608446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644806261 - 2⁷ = 644806133 is a prime.

It is a super-2 number, since 2×644806261² = 831550228449600242, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644806261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644804261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29309365 + ... + 29309386.

It is an arithmetic number, because the mean of its divisors is an integer number (175856256).

Almost surely, 2^644806261 is an apocalyptic number.

It is an amenable number.

644806261 is a deficient number, since it is larger than the sum of its proper divisors (58618763).

644806261 is a wasteful number, since it uses less digits than its factorization.

644806261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58618762.

The product of its (nonzero) digits is 55296, while the sum is 37.

The square root of 644806261 is about 25393.0356790991. The cubic root of 644806261 is about 863.9257431645.

The spelling of 644806261 in words is "six hundred forty-four million, eight hundred six thousand, two hundred sixty-one".