21665771 has 2 divisors, whose sum is σ = 21665772. Its totient is φ = 21665770.

The previous prime is 21665767. The next prime is 21665779. The reversal of 21665771 is 17756612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21665771 - 2² = 21665767 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21665779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832885 + 10832886.

It is an arithmetic number, because the mean of its divisors is an integer number (10832886).

Almost surely, 2^21665771 is an apocalyptic number.

21665771 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665771 is an equidigital number, since it uses as much as digits as its factorization.

21665771 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 17640, while the sum is 35.

The square root of 21665771 is about 4654.6504702287. The cubic root of 21665771 is about 278.7777120592. Note that the first 4 decimals are identical.

The spelling of 21665771 in words is "twenty-one million, six hundred sixty-five thousand, seven hundred seventy-one".