+ * congruent to 2 (mod 4); that the jump value is twice the
+ * product of two large primes; and that the starting point is
+ * at least %$3 \cdot 2^{N-2}$%. (Hence, if you multiply two
+ * such numbers, the product is at least
+ *
+ * %$9 \cdot 2^{2N-4} > 2^{2N-1}$%
+ *
+ * i.e., it will be (at least) a %$2 N$%-bit value.