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 A385993 #14 Aug 01 2025 11:05:49
%S A385993 1,2,1,2,3,4,3,2,1,2,3,4,5,4,3,2,3,4,5,6,7,8,7,6,5,6,7,6,5,4,3,2,1,2,
%T A385993 3,4,5,6,7,8,9,8,9,10,9,10,9,8,9,10,11,10,11,10,9,10,9,8,7,6,5,4,3,2,
%U A385993 3,4,5,6,7,8,9,10,11,12,11,12,11,12,13,12,13
%N A385993 a(n) is the number of distinct values appearing an odd number of times among A002487(0), ..., A002487(n).
%H A385993 Rémy Sigrist, <a href="/A385993/b385993.txt">Table of n, a(n) for n = 0..8192</a>
%H A385993 Rémy Sigrist, <a href="/A385993/a385993.gp.txt">PARI program</a>
%H A385993 <a href="/index/St#Stern">Index entries for sequences related to Stern's sequences</a>
%F A385993 a(n) = - Sum_{k = 1, n} (-1)^A091948(k).
%F A385993 abs(a(n+1) - a(n)) = 1.
%F A385993 a(n) = 1 iff n = 0 or n belongs to A004171.
%e A385993 Sequence begins:
%e A385993 n a(n) A091948(n)
%e A385993 -- ---- ----------
%e A385993 0 1 1
%e A385993 1 2 1
%e A385993 2 1 2
%e A385993 3 2 1
%e A385993 4 3 3
%e A385993 5 4 1
%e A385993 6 3 2
%e A385993 7 2 2
%e A385993 8 1 4
%e A385993 9 2 1
%e A385993 10 3 3
%e A385993 11 4 1
%e A385993 12 5 3
%o A385993 (PARI) \\ See Links section.
%Y A385993 Cf. A002487, A004171, A091948, A385991.
%K A385993 nonn
%O A385993 0,2
%A A385993 _Rémy Sigrist_, Jul 14 2025