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 A281258 #24 Aug 30 2022 13:56:20
%S A281258 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 A281258 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 A281258 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 A281258 Digital root of n*(n+1)*(n+2)/2.
%C A281258 Also zero together with period 9: repeat [3, 3, 3, 6, 6, 6, 9, 9, 9].
%C A281258 Also the decimal expansion of 334001/1001001.
%H A281258 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,-1,1,0,-1,1).
%F A281258 a(n) = A010888(A027480(n)).
%F A281258 From _Stefano Spezia_, Aug 30 2022: (Start)
%F A281258 G.f.: 3*x*(1 + 2*x^3 + 3*x^6)/((1 - x)*(1 + x^3 + x^6)).
%F A281258 a(n) = a(n-1) - a(n-3) + a(n-4) - a(n-6) + a(n-7) for n > 7. (End)
%t A281258 PadRight[{0},120,{9,3,3,3,6,6,6,9,9}] (* _Harvey P. Dale_, Mar 22 2018 *)
%Y A281258 Cf. A010888, A027480.
%K A281258 nonn,base,easy
%O A281258 0,2
%A A281258 _Peter M. Chema_, Jan 18 2017