Contributor: TOBIAS OLSSON (*I was looking for a faster sqr routine (still am), when I stumbled over all of your prime number programs. Although I don't know all about Turbo Pascal I do know how to make a faster Prime tester for Numbers < 31-bit, If you like it, copy it, use routines or whatever, but please think about leaving me credits This program builds on the (theory) that a prime is always equal to (X*6+1) or (X*6-1) this I read of in a magazine. And it seems to work... I have with this been able to take lead (I think) with 50% faster routine than the others by Tobias Olsson *) Unit Primtal; Interface Function Prime(Prim: LongInt): Boolean; implementation Function Prime(Prim: LongInt): Boolean; Var Z : Real; Max : LongInt; Divisor : LongInt; Begin Prime:= False; IF (Prim and 1) = 0 then Exit; Z := Sqrt(Prim); Max := Trunc(Z)+1; Divisor := 3; While Max> Divisor do Begin IF (Prim mod Divisor) = 0 then Exit; Inc(Divisor,2); IF (Prim mod Divisor) = 0 then Exit; Inc(Divisor,4); End; Prime := True; End; BEGIN END.