991307921 has 8 divisors (see below), whose sum is σ = 996705024. Its totient is φ = 985919760.

The previous prime is 991307857. The next prime is 991307929. The reversal of 991307921 is 129703199.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 991307921 - 2⁶ = 991307857 is a prime.

It is a super-3 number, since 3×991307921³ (a number of 28 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991307929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 415151 + ... + 417531.

It is an arithmetic number, because the mean of its divisors is an integer number (124588128).

Almost surely, 2^991307921 is an apocalyptic number.

It is an amenable number.

991307921 is a deficient number, since it is larger than the sum of its proper divisors (5397103).

991307921 is a wasteful number, since it uses less digits than its factorization.

991307921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4471.

The product of its (nonzero) digits is 30618, while the sum is 41.

The square root of 991307921 is about 31485.0428140093. The cubic root of 991307921 is about 997.0942048665.

The spelling of 991307921 in words is "nine hundred ninety-one million, three hundred seven thousand, nine hundred twenty-one".