21642191 has 2 divisors, whose sum is σ = 21642192. Its totient is φ = 21642190.

The previous prime is 21642169. The next prime is 21642193. The reversal of 21642191 is 19124612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21642191 - 2¹⁰ = 21641167 is a prime.

Together with 21642193, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21642191.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21642193) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821095 + 10821096.

It is an arithmetic number, because the mean of its divisors is an integer number (10821096).

Almost surely, 2^21642191 is an apocalyptic number.

21642191 is a deficient number, since it is larger than the sum of its proper divisors (1).

21642191 is an equidigital number, since it uses as much as digits as its factorization.

21642191 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 864, while the sum is 26.

The square root of 21642191 is about 4652.1168300033. The cubic root of 21642191 is about 278.6765391894.

The spelling of 21642191 in words is "twenty-one million, six hundred forty-two thousand, one hundred ninety-one".