~ Multiply by 3 and add 1 ( "!Enter a number (0 terminates) : " ? N: N. 0 > ^ ~ Read number and check > 0 0 C: ~ Initialize counter ( C. 20 \ 0 = [ "!" ] ~ New line every 20th number C. 1 + C: ~ Count items N. ! " " ~ Display an item N. 1 > ^ ~ Finished if N = 1 N. 2 \ 0 = [ N. 2 / M: ] ~ Item is even N. 2 \ 0 > [ 3 N. * 1 + M: ] ~ Item is odd M. N: ~ New value for N ) ) $