"SQUARE AND TRIANGULAR NUMBERS!"
( "ENTER A NUMBER " N ? = N. ^
     "S(" N. ! ") = " #S,N.; !
   "  T(" N. ! ") = " #T,N.; ! "!" )

$S %A 1 - [ #T,%A; #T,%A 1 -; + @ ] 1 @
$T %A 1 - [ #S,%A 1 -; 3 %A * 1 - + 2 / @ ] 1 @

$$