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 A161920 #14 May 17 2025 00:34:18 %S A161920 1,2,4,3,6,5,6,4,8,7,8,6,9,7,8,5,10,9,10,8,11,9,10,7,12,10,11,8,12,9, %T A161920 10,6,12,11,12,10,13,11,12,9,14,12,13,10,14,11,12,8,15,13,14,11,15,12, %U A161920 13,9,16,13,14,10,15,11,12,7,14,13,14,12,15,13,14,11,16,14,15,12,16 %N A161920 a(n) = A161511(A004760(n)). %C A161920 a(n) gives the one-based position of the first nonzero term on the row n-1 of A126441. %C A161920 Sequence A016116 can be used to identify the extracted subsequence by computing the number of terms to alternately extract and skip. [This comment is from the original submitter. I don't understand it. - _Antti Karttunen_, Oct 12 2009] %o A161920 (Python) %o A161920 def A161920(n): %o A161920 a, b = 1+(m:=n-1).bit_length(), 1 %o A161920 for i, j in enumerate(bin(m)[:1:-1], 1): %o A161920 if int(j): %o A161920 a += i-b %o A161920 b += 1 %o A161920 return a # _Chai Wah Wu_, Jul 26 2023 %Y A161920 a(n) = A161511(A004760(n)) = 1 + A055941(n-1) + A029837(n). %K A161920 nonn %O A161920 1,2 %A A161920 _Alford Arnold_, Jun 24 2009 %E A161920 Edited and extended by _Antti Karttunen_, Oct 12 2009