21808291 has 2 divisors, whose sum is σ = 21808292. Its totient is φ = 21808290.

The previous prime is 21808271. The next prime is 21808307. The reversal of 21808291 is 19280812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21808291 is a prime.

It is not a weakly prime, because it can be changed into another prime (21808231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904145 + 10904146.

It is an arithmetic number, because the mean of its divisors is an integer number (10904146).

Almost surely, 2^21808291 is an apocalyptic number.

21808291 is a deficient number, since it is larger than the sum of its proper divisors (1).

21808291 is an equidigital number, since it uses as much as digits as its factorization.

21808291 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 21808291 is about 4669.9347961187. The cubic root of 21808291 is about 279.3876541538.

The spelling of 21808291 in words is "twenty-one million, eight hundred eight thousand, two hundred ninety-one".