991157531 has 32 divisors (see below), whose sum is σ = 1241630208. Its totient is φ = 770353920.

The previous prime is 991157521. The next prime is 991157533. The reversal of 991157531 is 135751199.

It is not a de Polignac number, because 991157531 - 2⁶ = 991157467 is a prime.

It is a super-2 number, since 2×991157531² = 1964786502516031922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (991157533) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2122160 + ... + 2122626.

It is an arithmetic number, because the mean of its divisors is an integer number (38800944).

Almost surely, 2^991157531 is an apocalyptic number.

991157531 is a gapful number since it is divisible by the number (91) formed by its first and last digit.

991157531 is a deficient number, since it is larger than the sum of its proper divisors (250472677).

991157531 is a wasteful number, since it uses less digits than its factorization.

991157531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 851.

The product of its digits is 42525, while the sum is 41.

The square root of 991157531 is about 31482.6544465361. The cubic root of 991157531 is about 997.0437797066.

The spelling of 991157531 in words is "nine hundred ninety-one million, one hundred fifty-seven thousand, five hundred thirty-one".