12557667721 has 3 divisors (see below), whose sum is σ = 12557779783. Its totient is φ = 12557555660.

The previous prime is 12557667697. The next prime is 12557667757. The reversal of 12557667721 is 12776675521.

The square root of 12557667721 is 112061.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12776675521 = 419 ⋅30493259.

It can be written as a sum of positive squares in only one way, i.e., 11462057721 + 1095610000 = 107061^2 + 33100^2 .

It is a de Polignac number, because none of the positive numbers 2^k-12557667721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12557667781) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 56031 + ... + 168091.

Almost surely, 2^12557667721 is an apocalyptic number.

12557667721 is the 112061-st square number.

12557667721 is the 56031-st centered octagonal number.

It is an amenable number.

12557667721 is a deficient number, since it is larger than the sum of its proper divisors (112062).

12557667721 is an frugal number, since it uses more digits than its factorization.

12557667721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 224122 (or 112061 counting only the distinct ones).

The product of its digits is 1234800, while the sum is 49.

Multiplying 12557667721 by its sum of digits (49), we get a square (615325718329 = 784427²).

The spelling of 12557667721 in words is "twelve billion, five hundred fifty-seven million, six hundred sixty-seven thousand, seven hundred twenty-one".