20745209 has 2 divisors, whose sum is σ = 20745210. Its totient is φ = 20745208.

The previous prime is 20745203. The next prime is 20745211. The reversal of 20745209 is 90254702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11424400 + 9320809 = 3380^2 + 3053^2 .

It is a cyclic number.

It is not a de Polignac number, because 20745209 - 2²⁴ = 3967993 is a prime.

It is a Sophie Germain prime.

Together with 20745211, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is equal to p_1314875 and since 20745209 and 1314875 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (20745203) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10372604 + 10372605.

It is an arithmetic number, because the mean of its divisors is an integer number (10372605).

Almost surely, 2^20745209 is an apocalyptic number.

It is an amenable number.

20745209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20745209 is an equidigital number, since it uses as much as digits as its factorization.

20745209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5040, while the sum is 29.

The square root of 20745209 is about 4554.6908786437. The cubic root of 20745209 is about 274.7720822302.

The spelling of 20745209 in words is "twenty million, seven hundred forty-five thousand, two hundred nine".