21012091 has 2 divisors, whose sum is σ = 21012092. Its totient is φ = 21012090.

The previous prime is 21012077. The next prime is 21012127. The reversal of 21012091 is 19021012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21012091 - 2⁵ = 21012059 is a prime.

It is not a weakly prime, because it can be changed into another prime (21012991) 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, 10506045 + 10506046.

It is an arithmetic number, because the mean of its divisors is an integer number (10506046).

Almost surely, 2^21012091 is an apocalyptic number.

21012091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012091 is an equidigital number, since it uses as much as digits as its factorization.

21012091 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21012091 is about 4583.8947413744. The cubic root of 21012091 is about 275.9453569272.

The spelling of 21012091 in words is "twenty-one million, twelve thousand, ninety-one".