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 A081594 #31 Feb 26 2025 10:59:58
%S A081594 0,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10,11,4,5,6,7,8,9,10,11,12,13,6,
%T A081594 7,8,9,10,11,12,13,14,15,8,9,10,11,12,13,14,15,16,17,10,11,12,13,14,
%U A081594 15,16,17,18,19,12,13,14,15,16,17,18,19,20,21,14,15,16,17,18,19,20,21,22,23,16,17,18,19,20,21,22,23,24,25,18,19,20,21,22,23,24,25,26,27,20
%N A081594 Let n = 10x + y where 0 <= y <= 9, x >= 0. Then a(n) = 2x+y.
%H A081594 Vincenzo Librandi, <a href="/A081594/b081594.txt">Table of n, a(n) for n = 0..2000</a>
%H A081594 <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 A081594 a(n) = (2 * floor(n/10)) + (n modulo 10). - _Antti Karttunen_, Jun 22 2014
%F A081594 G.f.: -x*(7*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 23 2014
%F A081594 a(n) = n - 8*floor(n/10). [_Bruno Berselli_, Jun 24 2014]
%p A081594 A081594:=n->n-8*floor(n/10); seq(A081594(n), n=0..100); # _Wesley Ivan Hurt_, Jun 25 2014
%t A081594 CoefficientList[Series[-x (7 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 A081594 LinearRecurrence[{1,0,0,0,0,0,0,0,0,1,-1},{0,1,2,3,4,5,6,7,8,9,2},110] (* or *) Table[Range[n,n+9],{n,0,26,2}]//Flatten (* _Harvey P. Dale_, Jul 22 2021 *)
%o A081594 (MIT/GNU Scheme) (define (A081594 n) (+ (* 2 (floor->exact (/ n 10))) (modulo n 10))) ;; _Antti Karttunen_, Jun 22 2014
%o A081594 (PARI) my(n, x, y); vector(200, n, y=(n-1)%10; x=(n-1-y)\10; 2*x+y) \\ _Colin Barker_, Jun 24 2014
%o A081594 (Magma) [(n+4*y)/5 where y is n mod 10: n in [0..100]]; // _Bruno Berselli_, Jun 24 2014
%o A081594 (Sage) [n-8*floor(n/10) for n in (0..100)] # _Bruno Berselli_, Jun 24 2014
%Y A081594 Cf. A081502. Differs from A028897, A156230 and A244158 for the first time at n=100, which here is a(100) = 20.
%K A081594 nonn,easy
%O A081594 0,3
%A A081594 _N. J. A. Sloane_, Apr 22 2003
%E A081594 Terms up to n=100 added by _Antti Karttunen_, Jun 22 2014
%E A081594 G.f. revised by _Vincenzo Librandi_, Jun 25 2014