1317128721 has 4 divisors (see below), whose sum is σ = 1756171632. Its totient is φ = 878085812.

The previous prime is 1317128717. The next prime is 1317128749. The reversal of 1317128721 is 1278217131.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1317128721 - 2² = 1317128717 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1317138721) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 219521451 + ... + 219521456.

It is an arithmetic number, because the mean of its divisors is an integer number (439042908).

Almost surely, 2^1317128721 is an apocalyptic number.

It is an amenable number.

1317128721 is a deficient number, since it is larger than the sum of its proper divisors (439042911).

1317128721 is an equidigital number, since it uses as much as digits as its factorization.

1317128721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439042910.

The product of its digits is 4704, while the sum is 33.

The square root of 1317128721 is about 36292.2680608418. The cubic root of 1317128721 is about 1096.1653588502.

The spelling of 1317128721 in words is "one billion, three hundred seventeen million, one hundred twenty-eight thousand, seven hundred twenty-one".