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 A180592 #25 Nov 11 2022 18:45:54 %S A180592 0,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3, %T A180592 5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8, %U A180592 1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1,3,5,7,9,2,4,6,8,1 %N A180592 Digital root of 2n. %C A180592 Period 9. - _Robert G. Wilson v_, Sep 20 2010 %C A180592 Also digital root of A002276(n). - _Enrique Pérez Herrero_, Nov 05 2022 %H A180592 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,1). %F A180592 From _R. J. Mathar_, Nov 02 2010: (Start) %F A180592 a(n) = A010888(2*n). %F A180592 a(n) = a(n-9), n > 9. %F A180592 G.f.: -x*(2 + 4*x + 6*x^2 + 8*x^3 + x^4 + 3*x^5 + 5*x^6 + 7*x^7 + 9*x^8) / ( (x-1)*(1 + x + x^2)*(x^6 + x^3 + 1) ). (End) %t A180592 f[n_] := Mod[2 n - 1, 9] + 1; f[0] = 0; Array[f, 105, 0] (* _Robert G. Wilson v_, Sep 20 2010 *) %o A180592 (PARI) a(n)=if(n,(2*n-1)%9+1,0) \\ _Charles R Greathouse IV_, Aug 25 2014 %Y A180592 Cf. A007953, A010888, A180593, A180594, A180595, A180596, A180597, A180598, A180599. %K A180592 easy,nonn,base %O A180592 0,2 %A A180592 _Odimar Fabeny_, Sep 10 2010 %E A180592 More terms from _Robert G. Wilson v_, Sep 20 2010 %E A180592 Keyword:base and formulas from _R. J. Mathar_, Nov 02 2010