644542431556 has 9 divisors (see below), whose sum is σ = 1127952065149. Its totient is φ = 322270412944.

The previous prime is 644542431541. The next prime is 644542431569. The reversal of 644542431556 is 655134245446.

The square root of 644542431556 is 802834.

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

It can be written as a sum of positive squares in only one way, i.e., 607978872900 + 36563558656 = 779730^2 + 191216^2 .

It is a super-2 number, since 2×644542431556² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 1404960 + ... + 1806376.

Almost surely, 2^644542431556 is an apocalyptic number.

644542431556 is the 802834-th square number.

It is an amenable number.

644542431556 is a deficient number, since it is larger than the sum of its proper divisors (483409633593).

644542431556 is an frugal number, since it uses more digits than its factorization.

644542431556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 802838 (or 401419 counting only the distinct ones).

The product of its digits is 6912000, while the sum is 49.

Multiplying 644542431556 by its sum of digits (49), we get a square (31582579146244 = 5619838²).

The spelling of 644542431556 in words is "six hundred forty-four billion, five hundred forty-two million, four hundred thirty-one thousand, five hundred fifty-six".