91811561 has 4 divisors (see below), whose sum is σ = 95803392. Its totient is φ = 87819732.

The previous prime is 91811549. The next prime is 91811563. The reversal of 91811561 is 16511819.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16511819 = 857 ⋅19267.

It is a cyclic number.

It is not a de Polignac number, because 91811561 - 2⁶ = 91811497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91811563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1995881 + ... + 1995926.

It is an arithmetic number, because the mean of its divisors is an integer number (23950848).

Almost surely, 2^91811561 is an apocalyptic number.

It is an amenable number.

91811561 is a deficient number, since it is larger than the sum of its proper divisors (3991831).

91811561 is a wasteful number, since it uses less digits than its factorization.

91811561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3991830.

The product of its digits is 2160, while the sum is 32.

The square root of 91811561 is about 9581.8349495282. The cubic root of 91811561 is about 451.1273151180.

The spelling of 91811561 in words is "ninety-one million, eight hundred eleven thousand, five hundred sixty-one".