21116209 has 2 divisors, whose sum is σ = 21116210. Its totient is φ = 21116208.

The previous prime is 21116203. The next prime is 21116213. The reversal of 21116209 is 90261112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13432225 + 7683984 = 3665^2 + 2772^2 .

It is a cyclic number.

It is not a de Polignac number, because 21116209 - 2²³ = 12727601 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21116209.

It is not a weakly prime, because it can be changed into another prime (21116203) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10558104 + 10558105.

It is an arithmetic number, because the mean of its divisors is an integer number (10558105).

Almost surely, 2^21116209 is an apocalyptic number.

It is an amenable number.

21116209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21116209 is an equidigital number, since it uses as much as digits as its factorization.

21116209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21116209 is about 4595.2376434739. The cubic root of 21116209 is about 276.4003894390.

The spelling of 21116209 in words is "twenty-one million, one hundred sixteen thousand, two hundred nine".