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A081599 Let n = 10x + y where 0 <= y <= 9, x >= 0. Then a(n) = 8x+y.

%I A081599 #17 Feb 25 2025 15:53:16
%S A081599 0,1,2,3,4,5,6,7,8,9,8,9,10,11,12,13,14,15,16,17,16,17,18,19,20,21,22,
%T A081599 23,24,25,24,25,26,27,28,29,30,31,32,33,32,33,34,35,36,37,38,39,40,41,
%U A081599 40,41,42,43,44,45,46,47,48,49,48,49,50,51,52,53,54,55,56,57,56,57,58,59,60,61
%N A081599 Let n = 10x + y where 0 <= y <= 9, x >= 0. Then a(n) = 8x+y.
%H A081599 <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 A081599 G.f.: -x*(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 A081599 a(n) = n - 2*floor(n/10). - _Bruno Berselli_, Jun 24 2014
%p A081599 A081599 := proc(n)
%p A081599     local x,y ;
%p A081599     x := floor(n/10) ;
%p A081599     y := modp(n,10) ;
%p A081599     8*x+y ;
%p A081599 end proc:
%p A081599 seq(A081599(n),n=0..100) ; # _R. J. Mathar_, May 25 2023
%t A081599 Table[n-2*Floor[n/10],{n,0,80}] (* _Harvey P. Dale_, Nov 07 2017 *)
%o A081599 (PARI) my(n, x, y); vector(200, n, y=(n-1)%10; x=(n-1-y)\10; 8*x+y) \\ _Colin Barker_, Jun 24 2014
%o A081599 (Magma) k:=8; [n-(10-k)*Floor(n/10): n in [0..100]]; // _Bruno Berselli_, Jun 24 2014
%Y A081599 Cf. A081502. Different from A028898.
%K A081599 nonn,easy
%O A081599 0,3
%A A081599 _N. J. A. Sloane_, Apr 22 2003