21565091 has 2 divisors, whose sum is σ = 21565092. Its totient is φ = 21565090.

The previous prime is 21565087. The next prime is 21565111. The reversal of 21565091 is 19056512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21565091 - 2² = 21565087 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21565591) 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, 10782545 + 10782546.

It is an arithmetic number, because the mean of its divisors is an integer number (10782546).

Almost surely, 2^21565091 is an apocalyptic number.

21565091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21565091 is an equidigital number, since it uses as much as digits as its factorization.

21565091 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2700, while the sum is 29.

The square root of 21565091 is about 4643.8228863728. The cubic root of 21565091 is about 278.3452183562.

The spelling of 21565091 in words is "twenty-one million, five hundred sixty-five thousand, ninety-one".