my @count = 0, 0, 1; my $lock = Lock.new; put (1,2); for 3..17 -> $n { my @even = (2..^$n).grep: * %% 2; my @odd = (3..^$n).grep: so * % 2; @even.permutations.race.map: -> @e { quietly next if @e[0] == 8|14; my $nope = 0; for @odd.permutations -> @o { quietly next unless (@e[0] + @o[0]).is-prime; my @list; for (@list = (flat (roundrobin(@e, @o)), $n)).rotor(2 => -1) { $nope++ and last unless .sum.is-prime; } unless $nope { put '1 ', @list unless @count[$n]; $lock.protect({ @count[$n]++ }); } $nope = 0; } } } put "\n", @count[2..*];