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%I #21 Dec 27 2023 08:31:34
%S 4,5,3,7,8,6,1,2,0,13,14,12,16,17,15,10,11,9,22,23,21,25,26,24,19,20,
%T 18,31,32,30,34,35,33,28,29,27,40,41,39,43,44,42,37,38,36,49,50,48,52,
%U 53,51,46,47,45,58,59,57,61
%N Tersum n + 4.
%H <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,1,-1).
%F 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.
%t LinearRecurrence[{1, 0, 0, 0, 0, 0, 0, 0, 1, -1}, {4, 5, 3, 7, 8, 6, 1, 2, 0, 13, 14}, 80] (* _Jinyuan Wang_, Mar 10 2020 *)
%o (Python)
%o def tersum(a, b):
%o c, pow3 = 0, 1
%o while a + b > 0:
%o a, ra = divmod(a, 3)
%o b, rb = divmod(b, 3)
%o c, pow3 = c + pow3*((ra+rb)%3), pow3*3
%o return c
%o def a(n): return tersum(n, 4)
%o print([a(n) for n in range(58)]) # _Michael S. Branicky_, Apr 05 2021
%o (PARI) my(table=[4,4,1,4,4,1,-5,-5,-8]); a(n) = n + table[n%9+1]; \\ _Kevin Ryde_, Apr 05 2021
%Y Cf. A004489 (tersum array).
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_
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