\timing on
do $$
begin
  for i in 1..100000 loop
    perform 'a' ~ ('[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]' || i);
  end loop;
end$$;