The apparatus is made up of a board having four parellel columns of equal numbers of holes extending therethrough. A plurality of mutually distinguishable flexible pegs may be received in the holes. The pegs have indicium on both ends. The indicia on a given end of all of the pegs form a series, the indicium on one end of a given peg not corresponding in position in its series with the position of the indicium of the other end of the peg in its series. The number of pegs is less than the number of holes by at least the number of columns. The series are further divided into 4 subseries of equal numbers of pegs.