Here’s a (non–tail-recursive) solution in Factor that doesn’t. : collatz ( n -- length ) { { [ dup 1 = ] [ drop 0 ] } { [ dup even? ] [ 2 / colla

Here’s a (non–tail-recursive) solution in Factor that doesn’t. : collatz ( n -- length ) { { [ dup 1 = ] [ drop 0 ] } { [ dup even? ] [ 2 / collatz 1 + ] } [ 3 * 1 + collatz 1 + ] } cond ; Usage: 27 collatz