program additive_primes;
    loop for i in [i : i in [1..499] | additive_prime i] do
        nprint(lpad(str i, 4));
        if (n +:= 1) mod 10 = 0 then
            print;
        end if;
    end loop;
    print;
    print("There are " + str n + " additive primes less than 500.");

    op additive_prime(n);
        return prime n and prime digitsum n;
    end op;

    op prime(n);
        return n>=2 and not exists d in {2..floor sqrt n} | n mod d = 0;
    end op;

    op digitsum(n);
        loop while n>0;
            s +:= n mod 10;
            n div:= 10;
        end loop;
        return s;
    end op;
end program;