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%I #36 Dec 14 2023 06:14:45
%S 2,0,1,5,3,4,8,6,7,11,9,10,14,12,13,17,15,16,20,18,19,23,21,22,26,24,
%T 25,29,27,28,32,30,31,35,33,34,38,36,37,41,39,40,44,42,43,47,45,46,50,
%U 48,49,53,51,52,56,54,55,59,57,58,62,60,61,65,63,64,68,66,67
%N Tersum n + 2.
%C Tersum m + n: write m and n in base 3 and add mod 3 with no carries; e.g., 5 + 8 = "21" + "22" = "10" = 1.
%C Also Sprague-Grundy values for game of Wyt Queens.
%D E. R. Berlekamp, J. H. Conway and R. K. Guy, Winning Ways, Academic Press, NY, 2 vols., 1982, see p. 76.
%H Andreas Dress, Achim Flammenkamp, and Norbert Pink, <a href="http://dx.doi.org/10.1006/aama.1998.0632">Additive periodicity of the Sprague-Grundy function of certain Nim games</a>, Adv. Appl. Math., 22, p. 249-270 (1999).
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,1,-1).
%F Periodic with period and saltus 3: a(n) = 3*floor(n/3) + ((n+2) mod 3).
%F a(n) = n + 2*cos(2*n*Pi/3). - _Wesley Ivan Hurt_, Sep 27 2017
%F From _R. J. Mathar_, Dec 14 2017: (Start)
%F G.f.: ( 2+x^2+2*x^3-2*x ) / ( (1+x+x^2)*(x-1)^2 ).
%F a(n) = n + A099837(n) if n > 0. (End)
%F Sum_{n>=2} (-1)^n/a(n) = 2*Pi/(3*sqrt(3)) + log(2)/3 - 1/2. - _Amiram Eldar_, Aug 21 2023
%t a[n_] := If[Divisible[n, 3], n+2, n-1]; Table[a[n], {n, 0, 70}] (* _Jean-François Alcover_, Oct 25 2013 *)
%t LinearRecurrence[{1,0,1,-1},{2,0,1,5},70] (* _Harvey P. Dale_, Feb 07 2018 *)
%Y This sequence is row 2 of table A004481.
%Y Second column of triangle in A296339.
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_
%E Edited by _N. J. A. Sloane_ at the suggestion of _Philippe Deléham_, Nov 20 2007
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