CONST max = 2000
DIM SHARED stern(max + 2)

FUNCTION gcd (x, y)
    WHILE y
        t = y
        y = x MOD y
        x = t
    WEND
    gcd = x
END FUNCTION

SUB SternBrocot
    stern(1) = 1
    stern(2) = 1

    i = 2: n = 2: ub = UBOUND(stern)

    DO WHILE i < ub
        i = i + 1
        stern(i) = stern(n) + stern(n - 1)
        i = i + 1
        stern(i) = stern(n)
        n = n + 1
    LOOP
END SUB

SternBrocot

PRINT "The first 15 are: ";
FOR i = 1 TO 15
    PRINT stern(i); " ";
NEXT i

PRINT : PRINT
PRINT "  Index   First nr."
d = 1
FOR i = 1 TO max
    IF stern(i) = d THEN
        PRINT USING " ######"; i; stern(i)
        d = d + 1
        IF d = 11 THEN d = 100
        IF d = 101 THEN EXIT FOR
        i = 0
    END IF
NEXT i

PRINT : PRINT
d = 0
FOR i = 1 TO 1000
    IF gcd(stern(i), stern(i + 1)) <> 1 THEN
        d = gcd(stern(i), stern(i + 1))
        EXIT FOR
    END IF
NEXT i

IF d <> 0 THEN
    PRINT "GCD of two consecutive members of the series up to the 1000th member is 1"
ELSE
    PRINT "The GCD for index "; i; " and "; i + 1; " = "; d
END IF