let n be Nat; :: thesis: ( 53 divides n iff 53 divides (value ((mid ((digits (n,10)),2,(len (digits (n,10))))),10)) + (16 * ((digits (n,10)) . 0)) )
reconsider p = 53 as Prime by Th27;
A1: (10 * 16) - 1 = p * 3 ;
p,10 are_coprime by EULER_1:2;
hence ( 53 divides n iff 53 divides (value ((mid ((digits (n,10)),2,(len (digits (n,10))))),10)) + (16 * ((digits (n,10)) . 0)) ) by Th38, A1; :: thesis: verum