91221989 has 2 divisors, whose sum is σ = 91221990. Its totient is φ = 91221988.

The previous prime is 91221973. The next prime is 91222003. The reversal of 91221989 is 98912219.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 91049764 + 172225 = 9542^2 + 415^2 .

It is a cyclic number.

It is not a de Polignac number, because 91221989 - 2⁴ = 91221973 is a prime.

It is a super-2 number, since 2×91221989² = 16642902554232242, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91221919) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45610994 + 45610995.

It is an arithmetic number, because the mean of its divisors is an integer number (45610995).

Almost surely, 2^91221989 is an apocalyptic number.

It is an amenable number.

91221989 is a deficient number, since it is larger than the sum of its proper divisors (1).

91221989 is an equidigital number, since it uses as much as digits as its factorization.

91221989 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23328, while the sum is 41.

The square root of 91221989 is about 9551.0203119876. The cubic root of 91221989 is about 450.1595960662.

It can be divided in two parts, 9122 and 1989, that added together give a palindrome (11111).

The spelling of 91221989 in words is "ninety-one million, two hundred twenty-one thousand, nine hundred eighty-nine".