20505917 has 2 divisors, whose sum is σ = 20505918. Its totient is φ = 20505916.

The previous prime is 20505887. The next prime is 20505923. The reversal of 20505917 is 71950502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15792676 + 4713241 = 3974^2 + 2171^2 .

It is a cyclic number.

It is not a de Polignac number, because 20505917 - 2⁶ = 20505853 is a prime.

It is a super-3 number, since 3×20505917³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 20505917.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20505217) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10252958 + 10252959.

It is an arithmetic number, because the mean of its divisors is an integer number (10252959).

Almost surely, 2^20505917 is an apocalyptic number.

It is an amenable number.

20505917 is a deficient number, since it is larger than the sum of its proper divisors (1).

20505917 is an equidigital number, since it uses as much as digits as its factorization.

20505917 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3150, while the sum is 29.

The square root of 20505917 is about 4528.3459452652. The cubic root of 20505917 is about 273.7115128367.

The spelling of 20505917 in words is "twenty million, five hundred five thousand, nine hundred seventeen".