n separate points are given in the space, for each 3 points we put a yellow point in the centroid of them! whats the minimum set of yellow points ? there are exactly 3n-8 points Reference: http://www.artofproblemsolving.com/Forum/viewtopic.php?t=586434&p3472866&#p3472866 n= 3,4,5,.... 1,4,7,10,13,16.... A016777 : 3n+1, n=1,2,3.... APH