919978721 has 4 divisors (see below), whose sum is σ = 920343600. Its totient is φ = 919613844.

The previous prime is 919978691. The next prime is 919978739. The reversal of 919978721 is 127879919.

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 a de Polignac number, because none of the positive numbers 2^k-919978721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (919978121) 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, 178631 + ... + 183708.

It is an arithmetic number, because the mean of its divisors is an integer number (230085900).

Almost surely, 2^919978721 is an apocalyptic number.

It is an amenable number.

919978721 is a deficient number, since it is larger than the sum of its proper divisors (364879).

919978721 is a wasteful number, since it uses less digits than its factorization.

919978721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 364878.

The product of its digits is 571536, while the sum is 53.

The square root of 919978721 is about 30331.1510002506. The cubic root of 919978721 is about 972.5813277126.

The spelling of 919978721 in words is "nine hundred nineteen million, nine hundred seventy-eight thousand, seven hundred twenty-one".