21018091 has 2 divisors, whose sum is σ = 21018092. Its totient is φ = 21018090.

The previous prime is 21018079. The next prime is 21018097. The reversal of 21018091 is 19081012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21018091 - 2¹⁷ = 20887019 is a prime.

It is not a weakly prime, because it can be changed into another prime (21018097) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509045 + 10509046.

It is an arithmetic number, because the mean of its divisors is an integer number (10509046).

Almost surely, 2^21018091 is an apocalyptic number.

21018091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018091 is an equidigital number, since it uses as much as digits as its factorization.

21018091 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 22.

The square root of 21018091 is about 4584.5491599502. The cubic root of 21018091 is about 275.9716198152.

The spelling of 21018091 in words is "twenty-one million, eighteen thousand, ninety-one".