20991373456 has 45 divisors (see below), whose sum is σ = 42155338251. Its totient is φ = 10125652992.

The previous prime is 20991373411. The next prime is 20991373457. The reversal of 20991373456 is 65437319902.

The square root of 20991373456 is 144884.

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 93779856 + 20897593600 = 9684^2 + 144560^2 .

It is a super-2 number, since 2×20991373456² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20991373457) 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, 16805920 + ... + 16807168.

Almost surely, 2^20991373456 is an apocalyptic number.

20991373456 is the 144884-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20991373456

20991373456 is an abundant number, since it is smaller than the sum of its proper divisors (21163964795).

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

20991373456 is an frugal number, since it uses more digits than its factorization.

20991373456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2564 (or 1280 counting only the distinct ones).

The product of its (nonzero) digits is 1224720, while the sum is 49.

Multiplying 20991373456 by its sum of digits (49), we get a square (1028577299344 = 1014188²).

The spelling of 20991373456 in words is "twenty billion, nine hundred ninety-one million, three hundred seventy-three thousand, four hundred fifty-six".