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 A099990 #21 Jul 23 2023 06:07:29 %S A099990 1,-1,-1,-1,0,-1,-1,1,-1,-1,1,-1,0,0,-1,-1,1,1,-1,1,-1,-1,0,-1,0,1,-1, %T A099990 1,1,-1,-1,0,1,-1,1,-1,-1,0,1,-1,0,-1,1,1,-1,1,1,1,-1,0,-1,-1,-1,-1, %U A099990 -1,1,-1,1,0,1,0,1,0,-1,1,-1,1,0,-1,-1,1,1,1,0,-1,-1,0,1,-1,1,1,-1,-1,-1,0,0,-1,0,1,-1,-1,1,1,1,0,-1,-1,-1,-1,-1,1,1,1,0,1 %N A099990 a(n) = Moebius(2n+1). %H A099990 Amiram Eldar, <a href="/A099990/b099990.txt">Table of n, a(n) for n = 0..10000</a> %H A099990 J. W. Coltman, <a href="https://doi.org/10.1364/JOSA.44.000468">The Specification of Imaging Properties by Response to a Sine Wave Input</a>, J. Opt. Soc. Am., JOSA 44, 468 (1954). %H A099990 R. L. Lucke, <a href="https://doi.org/10.1364/AO.37.007248">Deriving the Coltman Correction for Transforming the Bar Transfer Function to the Optical Transfer Function (or the Contrast Transfer Function to the Modulation Transfer Function)</a>, Appl. Opt. 37, 7248 (1998). %t A099990 a[n_] := MoebiusMu[2*n + 1]; Array[a, 100, 0] (* _Amiram Eldar_, Jul 23 2023 *) %o A099990 (PARI) a(n) = moebius(2*n+1); \\ _Michel Marcus_, Aug 12 2021 %Y A099990 Bisection of A008683. %Y A099990 Cf. A099991. %K A099990 sign,easy %O A099990 0,1 %A A099990 _N. J. A. Sloane_, Nov 20 2004