20728517 has 2 divisors, whose sum is σ = 20728518. Its totient is φ = 20728516.

The previous prime is 20728501. The next prime is 20728531. The reversal of 20728517 is 71582702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14508481 + 6220036 = 3809^2 + 2494^2 .

It is a cyclic number.

It is not a de Polignac number, because 20728517 - 2⁴ = 20728501 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20728577) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10364258 + 10364259.

It is an arithmetic number, because the mean of its divisors is an integer number (10364259).

Almost surely, 2^20728517 is an apocalyptic number.

It is an amenable number.

20728517 is a deficient number, since it is larger than the sum of its proper divisors (1).

20728517 is an equidigital number, since it uses as much as digits as its factorization.

20728517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7840, while the sum is 32.

The square root of 20728517 is about 4552.8581133174. The cubic root of 20728517 is about 274.6983667958.

The spelling of 20728517 in words is "twenty million, seven hundred twenty-eight thousand, five hundred seventeen".