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 A297158 #11 Dec 23 2024 14:53:45
%S A297158 0,1,0,1,2,1,0,1,2,3,4,3,2,3,4,5,6,5,4,3,2,1,0,1,2,1,0,-1,-2,-1,0,1,2,
%T A297158 3,4,5,6,5,4,3,2,3,4,3,2,1,0,1,2,3,4,5,6,5,4,3,2,1,0,-1,-2,-1,0,1,2,3,
%U A297158 4,3,2,1,0,1,2,3,4,5,6,5,4,3,2,1,0,1,2,3,4,5,6,5,4,5,6,7,8,9,10,9,8,7,6,5,4,3,2,1
%N A297158 Ludic ladder sequence: a(n) = Sum_{k=1..n} (-1)^LudicPi(k), where LudicPi(n) = A192512(n)-1 gives the number of Ludic numbers > 1 and <= n.
%C A297158 This is an analogous sequence to A065358, but involving Ludic numbers (A003309) instead of primes. Compare the scatter-plots.
%H A297158 Antti Karttunen, <a href="/A297158/b297158.txt">Table of n, a(n) for n = 0..10000</a>
%H A297158 <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2018-February/018338.html">Discussion of SeqFan-list</a>, February 2018.
%H A297158 <a href="/index/Si#sieve">Index entries for sequences generated by sieves</a>
%F A297158 a(n) = Sum_{k=1..n} (-1)^(A192512(k)-1).
%o A297158 (Scheme, with memoization-macro definec)
%o A297158 (definec (A297158 n) (if (zero? n) n (+ (expt -1 (+ -1 (A192512 n))) (A297158 (- n 1)))))
%Y A297158 Cf. A003309, A192512.
%Y A297158 Differs from A065358 for the first time at n=19, where a(19) = 3, while A065358(19) = 5.
%K A297158 sign
%O A297158 0,5
%A A297158 _Antti Karttunen_, Feb 22 2018