644539566 has 16 divisors (see below), whose sum is σ = 1406268288. Its totient is φ = 195315000.

The previous prime is 644539561. The next prime is 644539573. The reversal of 644539566 is 665935446.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644539561) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4882810 + ... + 4882941.

It is an arithmetic number, because the mean of its divisors is an integer number (87891768).

Almost surely, 2^644539566 is an apocalyptic number.

644539566 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

644539566 is an abundant number, since it is smaller than the sum of its proper divisors (761728722).

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

644539566 is a wasteful number, since it uses less digits than its factorization.

644539566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9765767.

The product of its digits is 2332800, while the sum is 48.

The square root of 644539566 is about 25387.7837945733. The cubic root of 644539566 is about 863.8066187789.

The spelling of 644539566 in words is "six hundred forty-four million, five hundred thirty-nine thousand, five hundred sixty-six".