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 A126825 #23 Jan 06 2025 04:08:51 %S A126825 1,0,0,1,0,0,2,0,0,0,0,0,2,0,0,1,0,0,2,0,0,0,0,0,1,0,0,2,0,0,2,0,0,0, %T A126825 0,0,2,0,0,0,0,0,2,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,2,0,0,1,0,0,2,0, %U A126825 0,0,0,0,2,0,0,2,0,0,2,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,2,0,0,1,0,0,2,0,0 %N A126825 Ramanujan numbers (A000594) read mod 3. %H A126825 Amiram Eldar, <a href="/A126825/b126825.txt">Table of n, a(n) for n = 1..10000</a> %H A126825 R. P. Bambah and S. Chowla, <a href="http://dx.doi.org/10.1090/S0002-9904-1947-08913-8">Congruence properties of Ramanujan’s function tau(n)</a>, Bull. Amer. Math. Soc. 53 (1947), 950-955. %H A126825 John A. Ewell, <a href="http://dx.doi.org/10.1090/S0002-9939-99-05289-2">New representations of Ramanujan's tau function</a>, Proc. Amer. Math. Soc. 128 (2000), 723-726. %H A126825 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 A126825 a(4*n) = a(n) (see Corollary 2.2. p. 726 of Ewell link). - _Michel Marcus_, Dec 23 2012 %F A126825 a(n) = sigma(n) mod 3, for n coprime to 3. - _Michel Marcus_, Apr 26 2016 %p A126825 seq(modp(numtheory:-sigma(n),3)*(1-abs(mods(n-1,3))), n=1..105); # _Peter Luschny_, Apr 26 2016 %t A126825 Mod[RamanujanTau@ #, 3] & /@ Range@ 105 (* _Michael De Vlieger_, Apr 26 2016 *) %o A126825 (PARI) a(n) = ramanujantau(n) % 3; \\ _Amiram Eldar_, Jan 05 2025 %Y A126825 Cf. A000594, A000203. %K A126825 nonn %O A126825 1,7 %A A126825 _N. J. A. Sloane_, Feb 25 2007