20421209 has 2 divisors, whose sum is σ = 20421210. Its totient is φ = 20421208.

The previous prime is 20421187. The next prime is 20421223. The reversal of 20421209 is 90212402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12581209 + 7840000 = 3547^2 + 2800^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20421209 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20421229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10210604 + 10210605.

It is an arithmetic number, because the mean of its divisors is an integer number (10210605).

Almost surely, 2^20421209 is an apocalyptic number.

It is an amenable number.

20421209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20421209 is an equidigital number, since it uses as much as digits as its factorization.

20421209 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 20421209 is about 4518.9831820886. The cubic root of 20421209 is about 273.3341005663.

The spelling of 20421209 in words is "twenty million, four hundred twenty-one thousand, two hundred nine".