
theorem
  for a be odd Nat holds 3 divides 2|^a + 1
  proof
    let a be odd Nat;
    reconsider n = (a - 1)/2 as Nat;
    3 divides 2|^(2*n + 1) - 2 by NEWTON02:173; then
    3 divides ((2|^(2*n + 1) - 2) + 3) by WSIERP_1:4;
    hence thesis;
  end;
