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%I #24 Aug 30 2022 13:56:20
%S 0,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,
%T 9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,
%U 6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9,3,3,3,6,6,6,9,9,9
%N Digital root of n*(n+1)*(n+2)/2.
%C Also zero together with period 9: repeat [3, 3, 3, 6, 6, 6, 9, 9, 9].
%C Also the decimal expansion of 334001/1001001.
%H <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,-1,1,0,-1,1).
%F a(n) = A010888(A027480(n)).
%F From _Stefano Spezia_, Aug 30 2022: (Start)
%F G.f.: 3*x*(1 + 2*x^3 + 3*x^6)/((1 - x)*(1 + x^3 + x^6)).
%F a(n) = a(n-1) - a(n-3) + a(n-4) - a(n-6) + a(n-7) for n > 7. (End)
%t PadRight[{0},120,{9,3,3,3,6,6,6,9,9}] (* _Harvey P. Dale_, Mar 22 2018 *)
%Y Cf. A010888, A027480.
%K nonn,base,easy
%O 0,2
%A _Peter M. Chema_, Jan 18 2017
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