91157821 has 4 divisors (see below), whose sum is σ = 92256192. Its totient is φ = 90059452.

The previous prime is 91157797. The next prime is 91157861. The reversal of 91157821 is 12875119.

It is a happy number.

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: 12875119 = 191 ⋅67409.

It is a cyclic number.

It is not a de Polignac number, because 91157821 - 2¹⁹ = 90633533 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 (91157861) 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, 549061 + ... + 549226.

It is an arithmetic number, because the mean of its divisors is an integer number (23064048).

Almost surely, 2^91157821 is an apocalyptic number.

It is an amenable number.

91157821 is a deficient number, since it is larger than the sum of its proper divisors (1098371).

91157821 is a wasteful number, since it uses less digits than its factorization.

91157821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1098370.

The product of its digits is 5040, while the sum is 34.

The square root of 91157821 is about 9547.6604987819. The cubic root of 91157821 is about 450.0540198524.

The spelling of 91157821 in words is "ninety-one million, one hundred fifty-seven thousand, eight hundred twenty-one".