91281821 has 4 divisors (see below), whose sum is σ = 94429500. Its totient is φ = 88134144.

The previous prime is 91281811. The next prime is 91281829. The reversal of 91281821 is 12818219.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12818219 = 131 ⋅97849.

It can be written as a sum of positive squares in 2 ways, for example, as 39513796 + 51768025 = 6286^2 + 7195^2 .

It is a cyclic number.

It is not a de Polignac number, because 91281821 - 2²⁶ = 24172957 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 (91281829) 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, 1573796 + ... + 1573853.

It is an arithmetic number, because the mean of its divisors is an integer number (23607375).

Almost surely, 2^91281821 is an apocalyptic number.

It is an amenable number.

91281821 is a deficient number, since it is larger than the sum of its proper divisors (3147679).

91281821 is a wasteful number, since it uses less digits than its factorization.

91281821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3147678.

The product of its digits is 2304, while the sum is 32.

The square root of 91281821 is about 9554.1520293535. The cubic root of 91281821 is about 450.2579936228.

The spelling of 91281821 in words is "ninety-one million, two hundred eighty-one thousand, eight hundred twenty-one".