991238651 has 4 divisors (see below), whose sum is σ = 1067487792. Its totient is φ = 914989512.

The previous prime is 991238641. The next prime is 991238653. The reversal of 991238651 is 156832199.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 991238651 - 2¹⁰ = 991237627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991238653) 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, 38124551 + ... + 38124576.

It is an arithmetic number, because the mean of its divisors is an integer number (266871948).

Almost surely, 2^991238651 is an apocalyptic number.

991238651 is a deficient number, since it is larger than the sum of its proper divisors (76249141).

991238651 is a wasteful number, since it uses less digits than its factorization.

991238651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76249140.

The product of its digits is 116640, while the sum is 44.

The square root of 991238651 is about 31483.9427486457. The cubic root of 991238651 is about 997.0709795487.

The spelling of 991238651 in words is "nine hundred ninety-one million, two hundred thirty-eight thousand, six hundred fifty-one".