10 REM Modular inverse
20 LET E = 42
30 LET T = 2017
40 GOSUB 500
50 PRINT M
60 END
490 REM Calculate modular inverse
500 LET D = 0
510 IF E >= T THEN 600
520 LET B = E
530 LET C = 1
540 LET S1 = INT((T-B)/E)+1
550 LET B = B+S1*E
560 LET C = C+S1
570 LET B = B-T
580 IF B <> 1 THEN 540
590 LET D = C
600 LET M = D
610 RETURN