20728109 has 2 divisors, whose sum is σ = 20728110. Its totient is φ = 20728108.

The previous prime is 20728093. The next prime is 20728121. The reversal of 20728109 is 90182702.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20675209 + 52900 = 4547^2 + 230^2 .

It is a cyclic number.

It is not a de Polignac number, because 20728109 - 2⁴ = 20728093 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20728139) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10364054 + 10364055.

It is an arithmetic number, because the mean of its divisors is an integer number (10364055).

Almost surely, 2^20728109 is an apocalyptic number.

It is an amenable number.

20728109 is a deficient number, since it is larger than the sum of its proper divisors (1).

20728109 is an equidigital number, since it uses as much as digits as its factorization.

20728109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 20728109 is about 4552.8133060779. The cubic root of 20728109 is about 274.6965644854.

The spelling of 20728109 in words is "twenty million, seven hundred twenty-eight thousand, one hundred nine".