991225115521 has 8 divisors (see below), whose sum is σ = 998733767360. Its totient is φ = 983721857328.

The previous prime is 991225115479. The next prime is 991225115549. The reversal of 991225115521 is 125511522199.

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 991225115521 - 2²¹ = 991223018369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991225116521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 979086 + ... + 1714951.

It is an arithmetic number, because the mean of its divisors is an integer number (124841720920).

Almost surely, 2^991225115521 is an apocalyptic number.

It is an amenable number.

991225115521 is a deficient number, since it is larger than the sum of its proper divisors (7508651839).

991225115521 is a wasteful number, since it uses less digits than its factorization.

991225115521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2696823.

The product of its digits is 81000, while the sum is 43.

The spelling of 991225115521 in words is "nine hundred ninety-one billion, two hundred twenty-five million, one hundred fifteen thousand, five hundred twenty-one".