91639021 has 2 divisors, whose sum is σ = 91639022. Its totient is φ = 91639020.

The previous prime is 91639003. The next prime is 91639039. The reversal of 91639021 is 12093619.

It is a balanced prime because it is at equal distance from previous prime (91639003) and next prime (91639039).

It can be written as a sum of positive squares in only one way, i.e., 66748900 + 24890121 = 8170^2 + 4989^2 .

It is an emirp because it is prime and its reverse (12093619) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91639021 - 2¹⁹ = 91114733 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91639721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45819510 + 45819511.

It is an arithmetic number, because the mean of its divisors is an integer number (45819511).

Almost surely, 2^91639021 is an apocalyptic number.

It is an amenable number.

91639021 is a deficient number, since it is larger than the sum of its proper divisors (1).

91639021 is an equidigital number, since it uses as much as digits as its factorization.

91639021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 91639021 is about 9572.8272208371. The cubic root of 91639021 is about 450.8445391195.

The spelling of 91639021 in words is "ninety-one million, six hundred thirty-nine thousand, twenty-one".