21205291 has 2 divisors, whose sum is σ = 21205292. Its totient is φ = 21205290.

The previous prime is 21205279. The next prime is 21205297. The reversal of 21205291 is 19250212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21205291 is a prime.

It is not a weakly prime, because it can be changed into another prime (21205297) 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, 10602645 + 10602646.

It is an arithmetic number, because the mean of its divisors is an integer number (10602646).

Almost surely, 2^21205291 is an apocalyptic number.

21205291 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205291 is an equidigital number, since it uses as much as digits as its factorization.

21205291 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21205291 is about 4604.9203033277. The cubic root of 21205291 is about 276.7885234405.

The spelling of 21205291 in words is "twenty-one million, two hundred five thousand, two hundred ninety-one".