A161365 a(n) = 3/2 + 5*n - 5*(-1)^n/2.

9, 9, 19, 19, 29, 29, 39, 39, 49, 49, 59, 59, 69, 69, 79, 79, 89, 89, 99, 99, 109, 109, 119, 119, 129, 129, 139, 139, 149, 149, 159, 159, 169, 169, 179, 179, 189, 189, 199, 199, 209, 209, 219, 219, 229, 229, 239, 239, 249, 249, 259, 259, 269, 269, 279, 279, 289

Offset: 1

Author

Vincenzo Librandi, Nov 25 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Programs

Magma

I:=[9, 9, 19]; [n le 3 select I[n] else Self(n-1)+Self(n-2)-Self(n-3): n in [1..60]]; // Vincenzo Librandi, Mar 02 2012

Mathematica

LinearRecurrence[{1, 1, -1}, {9, 9, 19}, 60] (* Vincenzo Librandi, Mar 02 2012 *)
Table[3/2+5n-(5(-1)^n)/2,{n,60}] (* or *) nxt[{n_,a_}]:={n+1,10(n+1)-a-2}; NestList[nxt,{1,9},60][[;;,2]] (* Harvey P. Dale, Nov 04 2024 *)

PARI

for(n=1, 60, print1(3/2+5*n-5*(-1)^n/2", ")); \\ Vincenzo Librandi, Mar 02 2012

Formula

a(n) = 10*n - a(n-1) - 2, n > 1.

a(n+1) = A017377(floor(n/2)). - R. J. Mathar, Jan 05 2011

G.f.: x*(9+x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Jan 05 2011

Extensions

Definition rewritten by R. J. Mathar, Jan 05 2011