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A296881
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Numbers whose base-9 digits d(m), d(m-1), ..., d(0) have #(pits) < #(peaks); see Comments.
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4
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99, 100, 108, 109, 110, 117, 118, 119, 120, 126, 127, 128, 129, 130, 135, 136, 137, 138, 139, 140, 144, 145, 146, 147, 148, 149, 150, 153, 154, 155, 156, 157, 158, 159, 160, 189, 190, 191, 198, 199, 200, 201, 207, 208, 209, 210, 211, 216, 217, 218, 219, 220
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OFFSET
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1,1
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COMMENTS
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A pit is an index i such that d(i-1) > d(i) < d(i+1); a peak is an index i such that d(i-1) < d(i) > d(i+1). The sequences A296879-A296881 partition the natural numbers. See the guides at A296882 and A296712.
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LINKS
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EXAMPLE
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The base-9 digits of 220 are 2,6,4; here #(pits) = 0 and #(peaks) = 1, so 220 is in the sequence.
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MATHEMATICA
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z = 200; b = 9;
d[n_] := Differences[Sign[Differences[IntegerDigits[n, b]]]];
Select[Range [z], Count[d[#], -2] == Count[d[#], 2] &] (* A296879 *)
Select[Range [z], Count[d[#], -2] < Count[d[#], 2] &] (* A296880 *)
Select[Range [z], Count[d[#], -2] > Count[d[#], 2] &] (* A296881 *)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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