FRACTRAN in Perl 6. See http://rosettacode.org/wiki/Fractran

fractran.p6

sub fractran(@r) {
    sub ($n) {
	first Int, map (* *$n).narrow, @r
    }
}

say .[^20] given
2, fractran(<
    17/91 78/85 19/51 23/38 29/33 77/29 95/23 77/19 1/17 11/13 13/11 15/14 15/2 55/1
>) ... *;