The sequence is generated by following this pseudo-code:

A:  The first term is zero.
    Repeatedly apply:
        If the last term is *new* to the sequence so far then:
B:          The next term is zero.
        Otherwise:
C:          The next term is how far back this last term occured previously.



Example

Using A:

0
Using B:

0 0
Using C:

0 0 1
Using B:

0 0 1 0
Using C: (zero last occurred two steps back - before the one)

0 0 1 0 2
Using B:

0 0 1 0 2 0
Using C: (two last occurred two steps back - before the zero)

0 0 1 0 2 0 2 2
Using C: (two last occurred one step back)

0 0 1 0 2 0 2 2 1
Using C: (one last appeared six steps back)

0 0 1 0 2 0 2 2 1 6
...



Task

 Create a function/procedure/method/subroutine/... to generate the Van Eck sequence of numbers.
 Use it to display here, on this page:
 The first ten terms of the sequence.
 Terms 991 - to - 1000 of the sequence.


References

 Don't Know (the Van Eck Sequence) - Numberphile video.
 Wikipedia Article: Van Eck's Sequence.
  OEIS sequence: A181391.


0010 DIM eck#(0:1000)
0020 FOR i#:=1 TO 999 DO
0030   j#:=i#-1
0040   WHILE j#>0 AND eck#(i#)<>eck#(j#) DO j#:-1
0050   IF j#<>0 THEN eck#(i#+1):=i#-j#
0060 ENDFOR i#
0070 ZONE 5
0080 FOR i#:=1 TO 10 DO PRINT eck#(i#),
0090 PRINT
0100 FOR i#:=991 TO 1000 DO PRINT eck#(i#),
0110 PRINT
0120 END