21091871 has 2 divisors, whose sum is σ = 21091872. Its totient is φ = 21091870.

The previous prime is 21091867. The next prime is 21091891. The reversal of 21091871 is 17819012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21091871 - 2² = 21091867 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21091841) 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, 10545935 + 10545936.

It is an arithmetic number, because the mean of its divisors is an integer number (10545936).

Almost surely, 2^21091871 is an apocalyptic number.

21091871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21091871 is an equidigital number, since it uses as much as digits as its factorization.

21091871 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 29.

The square root of 21091871 is about 4592.5887035527. The cubic root of 21091871 is about 276.2941579527.

The spelling of 21091871 in words is "twenty-one million, ninety-one thousand, eight hundred seventy-one".