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%I #16 Apr 27 2016 03:40:29
%S 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 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 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 Ramanujan numbers (A000594) read mod 3.
%C a(4*n) = a(n) (see Corollary 2.2. p. 726 of Ewell link). - _Michel Marcus_, Dec 23 2012
%H 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 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 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 a(n) = sigma(n) mod 3, for n coprime to 3. - _Michel Marcus_, Apr 26 2016
%p seq(modp(numtheory:-sigma(n),3)*(1-abs(mods(n-1,3))), n=1..105); # _Peter Luschny_, Apr 26 2016
%t Mod[RamanujanTau@ #, 3] & /@ Range@ 105 (* _Michael De Vlieger_, Apr 26 2016 *)
%Y Cf. A000594, A000203.
%K nonn
%O 1,7
%A _N. J. A. Sloane_, Feb 25 2007
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