91999021 has 2 divisors, whose sum is σ = 91999022. Its totient is φ = 91999020.

The previous prime is 91999013. The next prime is 91999027. The reversal of 91999021 is 12099919.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 91489225 + 509796 = 9565^2 + 714^2 .

It is a cyclic number.

It is not a de Polignac number, because 91999021 - 2³ = 91999013 is a prime.

It is a super-3 number, since 3×91999021³ (a number of 25 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91999027) 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 as a sum of consecutive naturals, namely, 45999510 + 45999511.

It is an arithmetic number, because the mean of its divisors is an integer number (45999511).

Almost surely, 2^91999021 is an apocalyptic number.

It is an amenable number.

91999021 is a deficient number, since it is larger than the sum of its proper divisors (1).

91999021 is an equidigital number, since it uses as much as digits as its factorization.

91999021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13122, while the sum is 40.

The square root of 91999021 is about 9591.6120125868. The cubic root of 91999021 is about 451.4341422533.

The spelling of 91999021 in words is "ninety-one million, nine hundred ninety-nine thousand, twenty-one".