21660211 has 2 divisors, whose sum is σ = 21660212. Its totient is φ = 21660210.

The previous prime is 21660173. The next prime is 21660239. The reversal of 21660211 is 11206612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21660211 - 2⁷ = 21660083 is a prime.

It is not a weakly prime, because it can be changed into another prime (21660241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830105 + 10830106.

It is an arithmetic number, because the mean of its divisors is an integer number (10830106).

Almost surely, 2^21660211 is an apocalyptic number.

21660211 is a deficient number, since it is larger than the sum of its proper divisors (1).

21660211 is an equidigital number, since it uses as much as digits as its factorization.

21660211 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21660211 is about 4654.0531797563. The cubic root of 21660211 is about 278.7538628166.

Adding to 21660211 its reverse (11206612), we get a palindrome (32866823).

The spelling of 21660211 in words is "twenty-one million, six hundred sixty thousand, two hundred eleven".