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A043940
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Numbers k such that 1 and 3 occur juxtaposed in the base-8 representation of k but not of k+1.
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2
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11, 25, 75, 95, 139, 153, 207, 217, 267, 281, 331, 345, 395, 409, 459, 473, 523, 537, 587, 607, 651, 665, 767, 779, 793, 843, 857, 907, 921, 971, 985, 1035, 1049, 1099, 1119, 1163, 1177, 1231, 1241, 1291, 1305, 1355, 1369, 1419, 1433, 1483, 1497, 1547, 1561
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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SequencePosition[Table[If[SequenceCount[IntegerDigits[n, 8], {1, 3}]>0 || SequenceCount[IntegerDigits[n, 8], {3, 1}]>0, 1, 0], {n, 1400}], {1, 0}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 07 2020 *)
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PROG
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(Python)
def has13or31(n): o = oct(n); return "13" in o or "31" in o
def ok(n): return has13or31(n) and not has13or31(n+1)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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