991500551 has 4 divisors (see below), whose sum is σ = 991733400. Its totient is φ = 991267704.

The previous prime is 991500547. The next prime is 991500553. The reversal of 991500551 is 155005199.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 155005199 = 311 ⋅498409.

It is a cyclic number.

It is not a de Polignac number, because 991500551 - 2² = 991500547 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991500553) 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, 109916 + ... + 118593.

It is an arithmetic number, because the mean of its divisors is an integer number (247933350).

Almost surely, 2^991500551 is an apocalyptic number.

991500551 is a deficient number, since it is larger than the sum of its proper divisors (232849).

991500551 is a wasteful number, since it uses less digits than its factorization.

991500551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 232848.

The product of its (nonzero) digits is 10125, while the sum is 35.

The square root of 991500551 is about 31488.1017370054. The cubic root of 991500551 is about 997.1587854786.

The spelling of 991500551 in words is "nine hundred ninety-one million, five hundred thousand, five hundred fifty-one".