reserve a,b,k,m,n,s for Nat;
reserve c,c1,c2,c3 for Complex;
reserve i,j,z for Integer;
reserve p for Prime;
reserve x for object;

theorem Th30:
  card divisors(3|^(2*n+1),4,3) = n+1
  proof
    divisors(3|^(2*n+1),4,3) = { 3|^m: m is odd & m <= 2*n+1 } by Th26;
    hence thesis by Th28;
  end;
