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 A126828 #15 Jan 06 2025 01:23:47 %S A126828 1,57,9,67,51,27,23,78,0,72,12,36,35,15,54,70,45,0,38,15,45,36,69,54, %T A126828 61,51,0,2,3,0,17,9,27,54,39,0,74,60,72,9,6,54,41,75,0,45,75,63,21,75, %U A126828 0,77,54,0,45,12,18,9,24,54,50,78,0,37,3,0,62,18,54,36,18,0,65,6,63,35,33,54 %N A126828 Ramanujan numbers (A000594) read mod 81. %H A126828 Amiram Eldar, <a href="/A126828/b126828.txt">Table of n, a(n) for n = 1..10000</a> %H A126828 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 A126828 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 A126828 a(n) = (n^2+k)*sigma_7(n) with k=0 if gcd(n,3)=1 and k=9 if gcd(n,3)=2. - _Michel Marcus_, Apr 26 2016 %t A126828 Mod[RamanujanTau@ #, 81] & /@ Range@ 78 (* _Michael De Vlieger_, Apr 26 2016 *) %o A126828 (PARI) a(n) = ramanujantau(n) % 81; \\ _Amiram Eldar_, Jan 05 2025 %Y A126828 Cf. A000594, A013955. %K A126828 nonn %O A126828 1,2 %A A126828 _N. J. A. Sloane_, Feb 25 2007