20984209 has 2 divisors, whose sum is σ = 20984210. Its totient is φ = 20984208.

The previous prime is 20984207. The next prime is 20984219. The reversal of 20984209 is 90248902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20657025 + 327184 = 4545^2 + 572^2 .

It is a cyclic number.

It is not a de Polignac number, because 20984209 - 2¹ = 20984207 is a prime.

Together with 20984207, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20984207) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10492104 + 10492105.

It is an arithmetic number, because the mean of its divisors is an integer number (10492105).

Almost surely, 2^20984209 is an apocalyptic number.

It is an amenable number.

20984209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20984209 is an equidigital number, since it uses as much as digits as its factorization.

20984209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 20984209 is about 4580.8524315896. The cubic root of 20984209 is about 275.8232476443.

The spelling of 20984209 in words is "twenty million, nine hundred eighty-four thousand, two hundred nine".