644001813 has 32 divisors (see below), whose sum is σ = 1174252800. Its totient is φ = 339691968.

The previous prime is 644001797. The next prime is 644001833. The reversal of 644001813 is 318100446.

644001813 is a `hidden beast` number, since 644 + 0 + 0 + 1 + 8 + 13 = 666.

It is not a de Polignac number, because 644001813 - 2⁴ = 644001797 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

644001813 is a modest number, since divided by 1813 gives 644 as remainder.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644001833) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 128598 + ... + 133511.

It is an arithmetic number, because the mean of its divisors is an integer number (36695400).

Almost surely, 2^644001813 is an apocalyptic number.

644001813 is a gapful number since it is divisible by the number (63) formed by its first and last digit.

It is an amenable number.

644001813 is a deficient number, since it is larger than the sum of its proper divisors (530250987).

644001813 is a wasteful number, since it uses less digits than its factorization.

644001813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 262138 (or 262132 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 644001813 is about 25377.1908019781. The cubic root of 644001813 is about 863.5663212240.

The spelling of 644001813 in words is "six hundred forty-four million, one thousand, eight hundred thirteen".