644847861 has 16 divisors (see below), whose sum is σ = 987289088. Its totient is φ = 366735600.

The previous prime is 644847851. The next prime is 644847869. The reversal of 644847861 is 168748446.

644847861 = T₉₃ + T₉₄ + ... + T₁₅₆₉.

It is not a de Polignac number, because 644847861 - 2⁵ = 644847829 is a prime.

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 644847861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644847869) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 68335 + ... + 77196.

It is an arithmetic number, because the mean of its divisors is an integer number (61705568).

Almost surely, 2^644847861 is an apocalyptic number.

It is an amenable number.

644847861 is a deficient number, since it is larger than the sum of its proper divisors (342441227).

644847861 is a wasteful number, since it uses less digits than its factorization.

644847861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 145752.

The product of its digits is 1032192, while the sum is 48.

The square root of 644847861 is about 25393.8547881175. The cubic root of 644847861 is about 863.9443216328.

The spelling of 644847861 in words is "six hundred forty-four million, eight hundred forty-seven thousand, eight hundred sixty-one".