644215806 has 72 divisors (see below), whose sum is σ = 1545662664. Its totient is φ = 192767040.

The previous prime is 644215751. The next prime is 644215811. The reversal of 644215806 is 608512446.

644215806 is a `hidden beast` number, since 644 + 2 + 1 + 5 + 8 + 0 + 6 = 666.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 319341 + ... + 321351.

It is an arithmetic number, because the mean of its divisors is an integer number (21467537).

Almost surely, 2^644215806 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644215806, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (772831332).

644215806 is an abundant number, since it is smaller than the sum of its proper divisors (901446858).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644215806 is a wasteful number, since it uses less digits than its factorization.

644215806 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2106 (or 2066 counting only the distinct ones).

The product of its (nonzero) digits is 46080, while the sum is 36.

The square root of 644215806 is about 25381.4066986052. The cubic root of 644215806 is about 863.6619610598.

The spelling of 644215806 in words is "six hundred forty-four million, two hundred fifteen thousand, eight hundred six".