644664468100 has 81 divisors (see below), whose sum is σ = 1486366687407. Its totient is φ = 242645825280.

The previous prime is 644664468089. The next prime is 644664468101. The reversal of 644664468100 is 1864466446.

The square root of 644664468100 is 802910.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 15079348804 + 629585119296 = 122798^2 + 793464^2 .

It is a super-2 number, since 2×644664468100² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644664468101) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 136492339 + ... + 136497061.

Almost surely, 2^644664468100 is an apocalyptic number.

644664468100 is the 802910-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644664468100

644664468100 is an abundant number, since it is smaller than the sum of its proper divisors (841702219307).

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

644664468100 is an equidigital number, since it uses as much as digits as its factorization.

644664468100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9494 (or 4747 counting only the distinct ones).

The product of its (nonzero) digits is 2654208, while the sum is 49.

Multiplying 644664468100 by its sum of digits (49), we get a square (31588558936900 = 5620370²).

The spelling of 644664468100 in words is "six hundred forty-four billion, six hundred sixty-four million, four hundred sixty-eight thousand, one hundred".