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 A126812 #18 Jan 05 2025 01:05:40 %S A126812 1,0,0,0,2,0,0,0,1,0,0,0,2,0,0,0,2,0,0,0,0,0,0,0,3,0,0,0,2,0,0,0,0,0, %T A126812 0,0,2,0,0,0,2,0,0,0,2,0,0,0,1,0,0,0,2,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0, %U A126812 0,0,0,0,2,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,2,0,0,0,2,0,0,0,0 %N A126812 Ramanujan numbers (A000594) read mod 4. %D A126812 D. B. Lahiri, On Ramanujan's function tau(n) and divisor function sigma_k(n), I, Bulletin of the Calcutta Mathematical Society, Vol. 38 (1946), pp. 193-206; II, ibid., Vol. 39 (1947), pp. 33-51. %H A126812 Antti Karttunen, <a href="/A126812/b126812.txt">Table of n, a(n) for n = 1..65537</a> %H A126812 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 A126812 a(n) == n^2 * sigma_7(n) (mod 4) (Lahiri, 1946-1947). - _Amiram Eldar_, Jan 04 2025 %t A126812 Mod[#, 4] & /@ RamanujanTau@ Range@ 105 (* _Michael De Vlieger_, Nov 26 2017 *) %o A126812 (PARI) A126812(n) = (ramanujantau(n)%4); \\ _Antti Karttunen_, Nov 26 2017 %Y A126812 Cf. A000594, A008442, A013955, A098108, A126813, A126814. %K A126812 nonn %O A126812 1,5 %A A126812 _N. J. A. Sloane_, Feb 25 2007