1291916721 has 4 divisors (see below), whose sum is σ = 1722555632. Its totient is φ = 861277812.

The previous prime is 1291916707. The next prime is 1291916729. The reversal of 1291916721 is 1276191921.

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 not a de Polignac number, because 1291916721 - 2⁶ = 1291916657 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 1291916721.

It is not an unprimeable number, because it can be changed into a prime (1291916729) 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, 215319451 + ... + 215319456.

It is an arithmetic number, because the mean of its divisors is an integer number (430638908).

Almost surely, 2^1291916721 is an apocalyptic number.

It is an amenable number.

1291916721 is a deficient number, since it is larger than the sum of its proper divisors (430638911).

1291916721 is an equidigital number, since it uses as much as digits as its factorization.

1291916721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 430638910.

The product of its digits is 13608, while the sum is 39.

The square root of 1291916721 is about 35943.2430506764. The cubic root of 1291916721 is about 1089.1261185845.

The spelling of 1291916721 in words is "one billion, two hundred ninety-one million, nine hundred sixteen thousand, seven hundred twenty-one".