& (iter (for j from 0 to 160) (for p = (elt *Primes-List* j))
     (when (= (legendre -5 p) 1) (count 1)
       (format t "~%p = ~3D:      (p mod 20) = ~D." p (mod p 20))
       ) )


p =   2:   (p mod 20) = 2.  ;; Note 2 is prime, but not odd.

             ;; Here are the oddprimes:

p =   3:   (p mod 20) = 3.       p = 349:   (p mod 20) = 9.     p = 709:   (p mod 20) = 9.
p =   7:   (p mod 20) = 7.       p = 367:   (p mod 20) = 7.     p = 727:   (p mod 20) = 7.
p =  23:   (p mod 20) = 3.       p = 383:   (p mod 20) = 3.     p = 743:   (p mod 20) = 3.
p =  29:   (p mod 20) = 9.       p = 389:   (p mod 20) = 9.     p = 761:   (p mod 20) = 1.
p =  41:   (p mod 20) = 1.       p = 401:   (p mod 20) = 1.     p = 769:   (p mod 20) = 9.
p =  43:   (p mod 20) = 3.       p = 409:   (p mod 20) = 9.     p = 787:   (p mod 20) = 7.
p =  47:   (p mod 20) = 7.       p = 421:   (p mod 20) = 1.     p = 809:   (p mod 20) = 9.
p =  61:   (p mod 20) = 1.       p = 443:   (p mod 20) = 3.     p = 821:   (p mod 20) = 1.
p =  67:   (p mod 20) = 7.       p = 449:   (p mod 20) = 9.     p = 823:   (p mod 20) = 3.
p =  83:   (p mod 20) = 3.       p = 461:   (p mod 20) = 1.     p = 827:   (p mod 20) = 7.
p =  89:   (p mod 20) = 9.       p = 463:   (p mod 20) = 3.     p = 829:   (p mod 20) = 9.
p = 101:   (p mod 20) = 1.       p = 467:   (p mod 20) = 7.     p = 863:   (p mod 20) = 3.
p = 103:   (p mod 20) = 3.       p = 487:   (p mod 20) = 7.     p = 881:   (p mod 20) = 1.
p = 107:   (p mod 20) = 7.       p = 503:   (p mod 20) = 3.     p = 883:   (p mod 20) = 3.
p = 109:   (p mod 20) = 9.       p = 509:   (p mod 20) = 9.     p = 887:   (p mod 20) = 7.
p = 127:   (p mod 20) = 7.       p = 521:   (p mod 20) = 1.     p = 907:   (p mod 20) = 7.
p = 149:   (p mod 20) = 9.       p = 523:   (p mod 20) = 3.     p = 929:   (p mod 20) = 9.
p = 163:   (p mod 20) = 3.       p = 541:   (p mod 20) = 1.     p = 941:   (p mod 20) = 1.
p = 167:   (p mod 20) = 7.       p = 547:   (p mod 20) = 7.     p = 947:   (p mod 20) = 7.
p = 181:   (p mod 20) = 1.       p = 563:   (p mod 20) = 3.
p = 223:   (p mod 20) = 3.       p = 569:   (p mod 20) = 9.
p = 227:   (p mod 20) = 7.       p = 587:   (p mod 20) = 7.
p = 229:   (p mod 20) = 9.       p = 601:   (p mod 20) = 1.
p = 241:   (p mod 20) = 1.       p = 607:   (p mod 20) = 7.
p = 263:   (p mod 20) = 3.       p = 641:   (p mod 20) = 1.
p = 269:   (p mod 20) = 9.       p = 643:   (p mod 20) = 3.
p = 281:   (p mod 20) = 1.       p = 647:   (p mod 20) = 7.
p = 283:   (p mod 20) = 3.       p = 661:   (p mod 20) = 1.
p = 307:   (p mod 20) = 7.       p = 683:   (p mod 20) = 3.
p = 347:   (p mod 20) = 7.       p = 701:   (p mod 20) = 1.

             ;; So 80 primes out of the first 160 primes have -5 as a QR.