91011821 has 4 divisors (see below), whose sum is σ = 91126812. Its totient is φ = 90896832.

The previous prime is 91011803. The next prime is 91011887. The reversal of 91011821 is 12811019.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12811019 = 13 ⋅985463.

It can be written as a sum of positive squares in 2 ways, for example, as 63027721 + 27984100 = 7939^2 + 5290^2 .

It is a cyclic number.

It is not a de Polignac number, because 91011821 - 2¹⁸ = 90749677 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91011721) 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, 56300 + ... + 57893.

It is an arithmetic number, because the mean of its divisors is an integer number (22781703).

Almost surely, 2^91011821 is an apocalyptic number.

It is an amenable number.

91011821 is a deficient number, since it is larger than the sum of its proper divisors (114991).

91011821 is a wasteful number, since it uses less digits than its factorization.

91011821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 114990.

The product of its (nonzero) digits is 144, while the sum is 23.

The square root of 91011821 is about 9540.0115828022. The cubic root of 91011821 is about 449.8136199355.

The spelling of 91011821 in words is "ninety-one million, eleven thousand, eight hundred twenty-one".