[seqfan] 9 dots puzzle

[Dmitry Kamenetsky]

Hello fans,

Consider the 9 dots puzzle:
http://en.wikipedia.org/wiki/Thinking_outside_the_box#Nine_dots_puzzle
You are asked to join 9 dots (on integer coordinates) using 4 straight,
continuous lines (strokes).

I am now wondering: what is the smallest number of strokes required to join
all the points arranged in a NxN grid? The sequence starts with 1,3,4. How
to compute the rest of it?


Sincerely,
Dmitry Kamenetsky