1237791978721 has 3 divisors (see below), whose sum is σ = 1237793091283. Its totient is φ = 1237790866160.

The previous prime is 1237791978707. The next prime is 1237791978749. The reversal of 1237791978721 is 1278791977321.

The square root of 1237791978721 is 1112561.

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.

It can be written as a sum of positive squares in only one way, i.e., 193389737121 + 1044402241600 = 439761^2 + 1021960^2 .

It is not a de Polignac number, because 1237791978721 - 2²⁵ = 1237758424289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1237791978751) 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, 556281 + ... + 1668841.

Almost surely, 2^{1237791978721} is an apocalyptic number.

1237791978721 is the 1112561-st square number.

1237791978721 is the 556281-st centered octagonal number.

It is an amenable number.

1237791978721 is a deficient number, since it is larger than the sum of its proper divisors (1112562).

1237791978721 is an frugal number, since it uses more digits than its factorization.

1237791978721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2225122 (or 1112561 counting only the distinct ones).

The product of its digits is 18670176, while the sum is 64.

Multiplying 1237791978721 by its sum of digits (64), we get a square (79218686638144 = 8900488²).

It can be divided in two parts, 123779 and 1978721, that added together give a square (2102500 = 1450²).

The spelling of 1237791978721 in words is "one trillion, two hundred thirty-seven billion, seven hundred ninety-one million, nine hundred seventy-eight thousand, seven hundred twenty-one".