reserve n,k,b for Nat, i for Integer;

theorem
  53 divides n iff 53 divides value(digits(n,10)/^1,10) + 16*digits(n,10).0
  proof
    digits(n,10)/^1=mid(digits(n,10),2,len(digits(n,10))) by Th3;
    hence thesis by Th64;
  end;
