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 A073636 #42 Feb 16 2025 08:32:46
%S A073636 1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,
%T A073636 8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,
%U A073636 9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9,1,8,9
%N A073636 Period 3: repeat [1, 8, 9] ; Digital root of A000578(n) = n^3 for n >= 1.
%C A073636 a(n) is the decimal expansion of 70/37. [_Enrique Pérez Herrero_, Jul 28 2009]; corrected by _David A. Corneth_, Jun 30 2016
%H A073636 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DigitalRoot.html">Digital Root</a>.
%H A073636 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,1).
%F A073636 G.f.: x*(9*x^2+8*x+1)/(1-x^3). - _Ant King_, Apr 30 2013
%F A073636 From _Wesley Ivan Hurt_, Jun 30 2016: (Start)
%F A073636 a(n) = a(n-3) for n>3.
%F A073636 a(n) = 6 + 3*cos(2*n*Pi/3) - 7*sin(2*n*Pi/3)/sqrt(3). (End)
%p A073636 seq(op([1, 8, 9]), n=1..50); # _Wesley Ivan Hurt_, Jun 30 2016
%t A073636 n=3; su[x_] := Sum[IntegerDigits[x][[i]], {i, Length[IntegerDigits[x]]}]; Table[su[su[su[su[x^n]]]], {x, 100}]
%t A073636 NestWhile[Total[IntegerDigits[#]] &, #1, # > 9 &] & /@ (Range[87]^3) (* _Jayanta Basu_, Jul 03 2013 *)
%o A073636 (Magma) &cat [[1, 8, 9]^^30]; // _Wesley Ivan Hurt_, Jun 30 2016
%Y A073636 Cf. A000578, A004164, A010888, A021596. Digital roots of squares are in A056992.
%K A073636 nonn,base,easy
%O A073636 1,2
%A A073636 _Zak Seidov_, Sep 01 2002
%E A073636 Decimal expansion fraction corrected by _Ant King_, Apr 30 2013
%E A073636 Edited: name specified, offset changed from 0 to 1 (according to name), adjusted formula and g.f. for offset 1, digital root link added. - _Wolfdieter Lang_, Jan 05 2015