991550591 has 2 divisors, whose sum is σ = 991550592. Its totient is φ = 991550590.

The previous prime is 991550579. The next prime is 991550627. The reversal of 991550591 is 195055199.

It is a happy number.

It is a weak prime.

It is an emirp because it is prime and its reverse (195055199) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991550591 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991550291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495775295 + 495775296.

It is an arithmetic number, because the mean of its divisors is an integer number (495775296).

Almost surely, 2^991550591 is an apocalyptic number.

991550591 is a deficient number, since it is larger than the sum of its proper divisors (1).

991550591 is an equidigital number, since it uses as much as digits as its factorization.

991550591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 91125, while the sum is 44.

The square root of 991550591 is about 31488.8963128275. The cubic root of 991550591 is about 997.1755603848.

It can be divided in two parts, 9915 and 50591, that added together give a palindrome (60506).

The spelling of 991550591 in words is "nine hundred ninety-one million, five hundred fifty thousand, five hundred ninety-one".