A081594 Let n = 10x + y where 0 <= y <= 9, x >= 0. Then a(n) = 2x+y.

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, 7, 8, 9, 10, 11, 12, 13, 14, 15, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 10, 11, 12, 13, 14, 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

Offset: 0

Author

N. J. A. Sloane, Apr 22 2003

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..2000
• Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,0,1,-1).

Crossrefs

Cf. A081502. Differs from A028897, A156230 and A244158 for the first time at n=100, which here is a(100) = 20.

Programs

Magma

[(n+4*y)/5 where y is n mod 10: n in [0..100]]; // Bruno Berselli, Jun 24 2014

Maple

A081594:=n->n-8*floor(n/10); seq(A081594(n), n=0..100); # Wesley Ivan Hurt, Jun 25 2014

Mathematica

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 *)
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 *)

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

Sage

[n-8*floor(n/10) for n in (0..100)] # Bruno Berselli, Jun 24 2014

Formula

a(n) = (2 * floor(n/10)) + (n modulo 10). - Antti Karttunen, Jun 22 2014

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

a(n) = n - 8*floor(n/10). [Bruno Berselli, Jun 24 2014]

Extensions

Terms up to n=100 added by Antti Karttunen, Jun 22 2014

G.f. revised by Vincenzo Librandi, Jun 25 2014