21208091 has 2 divisors, whose sum is σ = 21208092. Its totient is φ = 21208090.

The previous prime is 21208087. The next prime is 21208097. The reversal of 21208091 is 19080212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21208091 - 2² = 21208087 is a prime.

It is not a weakly prime, because it can be changed into another prime (21208097) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10604045 + 10604046.

It is an arithmetic number, because the mean of its divisors is an integer number (10604046).

Almost surely, 2^21208091 is an apocalyptic number.

21208091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21208091 is an equidigital number, since it uses as much as digits as its factorization.

21208091 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 21208091 is about 4605.2243159264. The cubic root of 21208091 is about 276.8007055221.

The spelling of 21208091 in words is "twenty-one million, two hundred eight thousand, ninety-one".