21666791 has 2 divisors, whose sum is σ = 21666792. Its totient is φ = 21666790.

The previous prime is 21666779. The next prime is 21666811. The reversal of 21666791 is 19766612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21666791 - 2¹⁰ = 21665767 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21666731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833395 + 10833396.

It is an arithmetic number, because the mean of its divisors is an integer number (10833396).

Almost surely, 2^21666791 is an apocalyptic number.

21666791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666791 is an equidigital number, since it uses as much as digits as its factorization.

21666791 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 27216, while the sum is 38.

The square root of 21666791 is about 4654.7600367796. The cubic root of 21666791 is about 278.7820868370.

The spelling of 21666791 in words is "twenty-one million, six hundred sixty-six thousand, seven hundred ninety-one".