21402209 has 2 divisors, whose sum is σ = 21402210. Its totient is φ = 21402208.

The previous prime is 21402197. The next prime is 21402217. The reversal of 21402209 is 90220412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20729809 + 672400 = 4553^2 + 820^2 .

It is a cyclic number.

It is not a de Polignac number, because 21402209 - 2⁴ = 21402193 is a prime.

It is not a weakly prime, because it can be changed into another prime (21402229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10701104 + 10701105.

It is an arithmetic number, because the mean of its divisors is an integer number (10701105).

Almost surely, 2^21402209 is an apocalyptic number.

It is an amenable number.

21402209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21402209 is an equidigital number, since it uses as much as digits as its factorization.

21402209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21402209 is about 4626.2521548225. The cubic root of 21402209 is about 277.6426623536.

The spelling of 21402209 in words is "twenty-one million, four hundred two thousand, two hundred nine".