18978368644 has 9 divisors (see below), whose sum is σ = 33212627301. Its totient is φ = 9489046560.

The previous prime is 18978368639. The next prime is 18978368701. The reversal of 18978368644 is 44686387981.

The square root of 18978368644 is 137762.

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., 66618244 + 18911750400 = 8162^2 + 137520^2 .

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, 241084 + ... + 309964.

Almost surely, 2^18978368644 is an apocalyptic number.

18978368644 is the 137762-nd square number.

It is an amenable number.

18978368644 is a deficient number, since it is larger than the sum of its proper divisors (14234258657).

18978368644 is an frugal number, since it uses more digits than its factorization.

18978368644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137766 (or 68883 counting only the distinct ones).

The product of its digits is 55738368, while the sum is 64.

Multiplying 18978368644 by its sum of digits (64), we get a square (1214615593216 = 1102096²).

The spelling of 18978368644 in words is "eighteen billion, nine hundred seventy-eight million, three hundred sixty-eight thousand, six hundred forty-four".