FOR i% = -1 TO 100
        IF FNisprime(i%) PRINT ; i% " is prime"
      NEXT
      END

      DEF FNisprime(n%)
      IF n% <= 1 THEN = FALSE
      IF n% <= 3 THEN = TRUE
      IF (n% AND 1) = 0 THEN = FALSE
      LOCAL t%
      FOR t% = 3 TO SQR(n%) STEP 2
        IF n% MOD t% = 0 THEN = FALSE
      NEXT
      = TRUE