20985409 has 2 divisors, whose sum is σ = 20985410. Its totient is φ = 20985408.

The previous prime is 20985389. The next prime is 20985413. The reversal of 20985409 is 90458902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15681600 + 5303809 = 3960^2 + 2303^2 .

It is a cyclic number.

It is not a de Polignac number, because 20985409 - 2¹³ = 20977217 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20985439) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10492704 + 10492705.

It is an arithmetic number, because the mean of its divisors is an integer number (10492705).

Almost surely, 2^20985409 is an apocalyptic number.

It is an amenable number.

20985409 is a deficient number, since it is larger than the sum of its proper divisors (1).

20985409 is an equidigital number, since it uses as much as digits as its factorization.

20985409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 20985409 is about 4580.9834097058. The cubic root of 20985409 is about 275.8285052737.

The spelling of 20985409 in words is "twenty million, nine hundred eighty-five thousand, four hundred nine".