21242591 has 2 divisors, whose sum is σ = 21242592. Its totient is φ = 21242590.

The previous prime is 21242569. The next prime is 21242629. The reversal of 21242591 is 19524212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21242591 - 2⁶ = 21242527 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21242591.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21242521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10621295 + 10621296.

It is an arithmetic number, because the mean of its divisors is an integer number (10621296).

Almost surely, 2^21242591 is an apocalyptic number.

21242591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21242591 is an equidigital number, since it uses as much as digits as its factorization.

21242591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 26.

The square root of 21242591 is about 4608.9685397060. The cubic root of 21242591 is about 276.9507182503.

The spelling of 21242591 in words is "twenty-one million, two hundred forty-two thousand, five hundred ninety-one".