theorem Th22:
  n divides 325 implies n = 1 or n = 5 or n = 13 or n = 25 or n = 65 or n = 325
  proof
    assume n divides 325;
    then n divides 13*25;
    then consider a,b such that
A1: a divides 13 & b divides 25 and
A2: n = a*b by Lem1;
    (a = 1 or a = 13) &
    (b = 1 or b = 5 or b = 25) by A1,Th13,XPRIMES1:13;
    hence thesis by A2;
  end;
