Hey Guys, there was a question in Round 2 of the HackWithInfy Contest which I feel is quite nice and I wasn't able to think of any possible solution to it. So the question goes like that:-

We have defined a function f(x) = sum of all the digits of x. Now,

0 <= i <= N

0 <= j <= N

We have to count how many pairs are there which satisfy the condition that f(i) + f(j) is a prime.

Constraints:- 0 <= N <= 10^50

Example:-

1) N = 2

pairs = 2

2) N = 3

pairs = 4

Can anyone suggest some possible method to solve this question??