20728121 has 2 divisors, whose sum is σ = 20728122. Its totient is φ = 20728120.

The previous prime is 20728109. The next prime is 20728133. The reversal of 20728121 is 12182702.

It is a balanced prime because it is at equal distance from previous prime (20728109) and next prime (20728133).

It can be written as a sum of positive squares in only one way, i.e., 20070400 + 657721 = 4480^2 + 811^2 .

It is a cyclic number.

It is not a de Polignac number, because 20728121 - 2²² = 16533817 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20728921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10364060 + 10364061.

It is an arithmetic number, because the mean of its divisors is an integer number (10364061).

Almost surely, 2^20728121 is an apocalyptic number.

It is an amenable number.

20728121 is a deficient number, since it is larger than the sum of its proper divisors (1).

20728121 is an equidigital number, since it uses as much as digits as its factorization.

20728121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 20728121 is about 4552.8146239442. The cubic root of 20728121 is about 274.6966174949.

The spelling of 20728121 in words is "twenty million, seven hundred twenty-eight thousand, one hundred twenty-one".