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 A126813 #19 Sep 09 2022 18:22:09 %S A126813 1,0,4,0,6,0,0,0,5,0,4,0,6,0,0,0,2,0,4,0,0,0,0,0,7,0,0,0,6,0,0,0,0,0, %T A126813 0,0,6,0,0,0,2,0,4,0,6,0,0,0,1,0,0,0,6,0,0,0,0,0,4,0,6,0,0,0,4,0,4,0, %U A126813 0,0,0,0,2,0,4,0,0,0,0,0,1,0,4,0,4,0,0,0,2,0,0,0,0,0,0,0,2,0,4,0,6,0,0,0,0 %N A126813 Ramanujan numbers (A000594) read mod 8. %H A126813 Antti Karttunen, <a href="/A126813/b126813.txt">Table of n, a(n) for n = 1..65537</a> %H A126813 R. P. Bambah, S. Chowla and H. Gupta, <a href="http://dx.doi.org/10.1090/S0002-9904-1947-08870-4">A congruence property of Ramanujan’s function tau(n)</a>, Bull. Amer. Math. Soc. 53 (1947), 766-767. %H A126813 H. P. F. Swinnerton-Dyer, <a href="http://dx.doi.org/10.1007/978-3-540-37802-0_1">On l-adic representations and congruences for coefficients of modular forms</a>, pp. 1-55 of Modular Functions of One Variable III (Antwerp 1972), Lect. Notes Math., 350, 1973. %F A126813 For all odd n, a(n) = sigma(n) mod 8 = A105827(n). - _Michel Marcus_, Apr 25 2016 %t A126813 Mod[RamanujanTau@ #, 8] &@ Range@ 120 (* _Michael De Vlieger_, Apr 25 2016 *) %o A126813 (PARI) A126813(n) = (ramanujantau(n)%8); \\ _Antti Karttunen_, Nov 26 2017 %o A126813 (PARI) a(n)=my(e=valuation(n,2)); ramanujantau(2^e)*sigma(n>>e)%8 \\ _Charles R Greathouse IV_, Sep 09 2022 %Y A126813 Cf. A000594, A000203, A098108, A105827, A126812, A126814. %K A126813 nonn,easy %O A126813 1,3 %A A126813 _N. J. A. Sloane_, Feb 25 2007