The first 10 take less than a quarter second. 11 through 13, a little under 30 seconds. Drops off a cliff after that.
sub useful ($n) {
(|$n).map: {
my $p = 1 +< ( 1 +< $_ );
^$p .first: ($p - *).is-prime
}
}
put useful 1..10;
put useful 11..13;
1 3 5 15 5 59 159 189 569 105
1557 2549 2439