644028720196 has 27 divisors (see below), whose sum is σ = 1135086616951. Its totient is φ = 319734417824.

The previous prime is 644028720191. The next prime is 644028720197. The reversal of 644028720196 is 691027820446.

The square root of 644028720196 is 802514.

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 162481548100 + 481547172096 = 403090^2 + 693936^2 .

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644028720191) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 239147826 + ... + 239150518.

Almost surely, 2^644028720196 is an apocalyptic number.

644028720196 is the 802514-th square number.

It is an amenable number.

644028720196 is a deficient number, since it is larger than the sum of its proper divisors (491057896755).

644028720196 is an frugal number, since it uses more digits than its factorization.

644028720196 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5688 (or 2844 counting only the distinct ones).

The product of its (nonzero) digits is 1161216, while the sum is 49.

Multiplying 644028720196 by its sum of digits (49), we get a square (31557407289604 = 5617598²).

It can be divided in two parts, 644028 and 720196, that added together give a square (1364224 = 1168²).

The spelling of 644028720196 in words is "six hundred forty-four billion, twenty-eight million, seven hundred twenty thousand, one hundred ninety-six".