This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A137708 #19 May 16 2025 15:52:03
%S A137708 1,2,5,6,7,8,11,12,15,16,17,18,21,22,23,24,27,28,31,32,33,34,37,38,41,
%T A137708 42,43,44,47,48,49,50,53,54,57,58,59,60,63,64,65,66,69,70,73,74,75,76,
%U A137708 79,80,83,84,85,86,89,90,91,92,95,96,99,100,101,102,105,106,109,110,111
%N A137708 Secondary Lower Wythoff Sequence.
%C A137708 This sequence is the ordered union of odd numbered columns of the Wythoff secondary array, A137707. See A137707 for complementary equations of which this sequence is a solution.
%F A137708 a(2n) = 2*A000201(n) = a(2n-1)+1; A000201 is the lower Wythoff sequence.
%e A137708 The lower Wythoff sequence begins with 1,3,4,6,8,9,...
%e A137708 Double these: 2,6,8,12,16,18...; subtract 1: 1,5,7,11,15,17;
%e A137708 Then merge: 1,2,5,6,7,8,11,12,15,16,17,18,...
%t A137708 Union[Flatten[{#, # - 1}]] &[2 Array[Floor[#*GoldenRatio] &, 20]] (* _Peter J. C. Moses_, May 12 2025 *)
%o A137708 (Python)
%o A137708 from math import isqrt
%o A137708 def A137708(n): return ((m:=n+1>>1)+isqrt(5*m**2)&-2)-(n&1) # _Chai Wah Wu_, Aug 11 2022
%Y A137708 Cf. A035513, A137709.
%K A137708 nonn,easy
%O A137708 1,2
%A A137708 _Clark Kimberling_, Feb 07 2008
%E A137708 a(37)=59 corrected by _Georg Fischer_, Nov 24 2022