91909981 has 4 divisors (see below), whose sum is σ = 93416764. Its totient is φ = 90403200.

The previous prime is 91909969. The next prime is 91910017. The reversal of 91909981 is 18990919.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 20169081 + 71740900 = 4491^2 + 8470^2 .

It is a cyclic number.

It is not a de Polignac number, because 91909981 - 2¹⁵ = 91877213 is a prime.

It is a super-2 number, since 2×91909981² = 16894889214840722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91909901) 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, 753300 + ... + 753421.

It is an arithmetic number, because the mean of its divisors is an integer number (23354191).

Almost surely, 2^91909981 is an apocalyptic number.

It is an amenable number.

91909981 is a deficient number, since it is larger than the sum of its proper divisors (1506783).

91909981 is a wasteful number, since it uses less digits than its factorization.

91909981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1506782.

The product of its (nonzero) digits is 52488, while the sum is 46.

The square root of 91909981 is about 9586.9693334234. The cubic root of 91909981 is about 451.2884571138.

The spelling of 91909981 in words is "ninety-one million, nine hundred nine thousand, nine hundred eighty-one".