P415
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Titanic Sets

ℹ️Published on Sunday, 17th February 2013, 10:00 am; Solved by 358;
Difficulty rating: 100%

A set of lattice points $S$ is called a titanic set if there exists a line passing through exactly two points in $S$.

An example of a titanic set is $S = \{(0, 0), (0, 1), (0, 2), (1, 1), (2, 0), (1, 0)\}$, where the line passing through $(0, 1)$ and $(2, 0)$ does not pass through any other point in $S$.

On the other hand, the set $\{(0, 0), (1, 1), (2, 2), (4, 4)\}$ is not a titanic set since the line passing through any two points in the set also passes through the other two.

For any positive integer $N$, let $T(N)$ be the number of titanic sets $S$ whose every point $(x, y)$ satisfies $0 \leq x, y \leq N$. It can be verified that $T(1) = 11$, $T(2) = 494$, $T(4) = 33554178$, $T(111) \bmod 10^8 = 13500401$ and $T(10^5) \bmod 10^8 = 63259062$.

Find $T(10^{11})\bmod 10^8$.



Soluzione

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