91221726978 has 54 divisors (see below), whose sum is σ = 199138022811. Its totient is φ = 30179579904.

The previous prime is 91221726961. The next prime is 91221726983. The reversal of 91221726978 is 87962712219.

91221726978 is a `hidden beast` number, since 91 + 221 + 7 + 269 + 78 = 666.

It can be written as a sum of positive squares in 5 ways, for example, as 71611365609 + 19610361369 = 267603^2 + 140037^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=213567.

It is an unprimeable number.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 329320176 + ... + 329320452.

Almost surely, 2^91221726978 is an apocalyptic number.

91221726978 is an abundant number, since it is smaller than the sum of its proper divisors (107916295833).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

91221726978 is an equidigital number, since it uses as much as digits as its factorization.

91221726978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1076 (or 539 counting only the distinct ones).

The product of its digits is 1524096, while the sum is 54.

The spelling of 91221726978 in words is "ninety-one billion, two hundred twenty-one million, seven hundred twenty-six thousand, nine hundred seventy-eight".