A043160 Numbers k such that 1 and 3 occur juxtaposed in the base-8 representation of k but not of k-1.

11, 25, 75, 88, 139, 153, 200, 217, 267, 281, 331, 345, 395, 409, 459, 473, 523, 537, 587, 600, 651, 665, 704, 779, 793, 843, 857, 907, 921, 971, 985, 1035, 1049, 1099, 1112, 1163, 1177, 1224, 1241, 1291, 1305, 1355, 1369, 1419, 1433, 1483, 1497, 1547, 1561

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007094, A043940.

Programs

Mathematica

SequencePosition[Table[If[SequenceCount[IntegerDigits[n,8],{1,3}]>0 || SequenceCount[ IntegerDigits[n,8],{3,1}]>0,1,0],{n,1600}],{0,1}][[All,2]] (* Harvey P. Dale, Nov 11 2022 *)

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