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 A081595 #18 Aug 27 2025 08:02:08
%S A081595 0,1,2,3,4,5,6,7,8,9,4,5,6,7,8,9,10,11,12,13,8,9,10,11,12,13,14,15,16,
%T A081595 17,12,13,14,15,16,17,18,19,20,21,16,17,18,19,20,21,22,23,24,25,20,21,
%U A081595 22,23,24,25,26,27,28,29,24,25,26,27,28,29,30,31,32,33,28,29,30,31,32,33,34,35
%N A081595 Let n = 10x + y where 0 <= y <= 9, x >= 0. Then a(n) = 4x+y.
%H A081595 Vincenzo Librandi, <a href="/A081595/b081595.txt">Table of n, a(n) for n = 0..2000</a>
%H A081595 <a href="/index/Rec#order_11">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,0,1,-1).
%F A081595 G.f.: -x*(5*x^9 -x^8 -x^7 -x^6 -x^5 -x^4 -x^3 -x^2 -x -1) / ((x -1)^2*(x +1)*(x^4 -x^3 +x^2 -x +1)*(x^4 +x^3 +x^2 +x +1)). - _Colin Barker_, Jun 24 2014
%F A081595 a(n) = n - 6*floor(n/10). [_Bruno Berselli_, Jun 24 2014]
%t A081595 CoefficientList[Series[-x (5 x^9 - x^8 - x^7 - x^6 - x^5 - x^4 - x^3 - x^2 - x - 1)/((x - 1)^2 (x + 1) (x^4 - x^3 + x^2 - x + 1) (x^4 + x^3 + x^2 + x + 1)), {x, 0, 150}], x] (* _Vincenzo Librandi_, Jun 25 2014 *)
%t A081595 LinearRecurrence[{1,0,0,0,0,0,0,0,0,1,-1},{0,1,2,3,4,5,6,7,8,9,4},80] (* _Harvey P. Dale_, Sep 17 2023 *)
%o A081595 (PARI) my(n, x, y); vector(200, n, y=(n-1)%10; x=(n-1-y)\10; 4*x+y) \\ _Colin Barker_, Jun 24 2014
%o A081595 (Magma) k:=4; [n-(10-k)*Floor(n/10): n in [0..100]]; // _Bruno Berselli_, Jun 24 2014
%Y A081595 Cf. A081502. Starts to differ from A028899 at a(100).
%K A081595 nonn,changed
%O A081595 0,3
%A A081595 _N. J. A. Sloane_, Apr 22 2003