21908791 has 2 divisors, whose sum is σ = 21908792. Its totient is φ = 21908790.

The previous prime is 21908771. The next prime is 21908797. The reversal of 21908791 is 19780912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21908791 - 2⁹ = 21908279 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 21908791.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21908797) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10954395 + 10954396.

It is an arithmetic number, because the mean of its divisors is an integer number (10954396).

Almost surely, 2^21908791 is an apocalyptic number.

21908791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21908791 is an equidigital number, since it uses as much as digits as its factorization.

21908791 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21908791 is about 4680.6827493433. The cubic root of 21908791 is about 279.8161675976.

The spelling of 21908791 in words is "twenty-one million, nine hundred eight thousand, seven hundred ninety-one".