A043940 Numbers k such that 1 and 3 occur juxtaposed in the base-8 representation of k but not of k+1.
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
Offset: 1
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
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 *) -
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) print([k for k in range(1600) if ok(k)]) # Michael S. Branicky, Nov 25 2021