91981621 has 2 divisors, whose sum is σ = 91981622. Its totient is φ = 91981620.

The previous prime is 91981613. The next prime is 91981627. The reversal of 91981621 is 12618919.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 68807025 + 23174596 = 8295^2 + 4814^2 .

It is a cyclic number.

It is not a de Polignac number, because 91981621 - 2³ = 91981613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91981627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45990810 + 45990811.

It is an arithmetic number, because the mean of its divisors is an integer number (45990811).

Almost surely, 2^91981621 is an apocalyptic number.

It is an amenable number.

91981621 is a deficient number, since it is larger than the sum of its proper divisors (1).

91981621 is an equidigital number, since it uses as much as digits as its factorization.

91981621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 37.

The square root of 91981621 is about 9590.7049271678. The cubic root of 91981621 is about 451.4056801775.

The spelling of 91981621 in words is "ninety-one million, nine hundred eighty-one thousand, six hundred twenty-one".