A168401 a(n) = 4 + 9*floor(n/2).

4, 13, 13, 22, 22, 31, 31, 40, 40, 49, 49, 58, 58, 67, 67, 76, 76, 85, 85, 94, 94, 103, 103, 112, 112, 121, 121, 130, 130, 139, 139, 148, 148, 157, 157, 166, 166, 175, 175, 184, 184, 193, 193, 202, 202, 211, 211, 220, 220, 229, 229, 238, 238, 247, 247, 256, 256

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).

Crossrefs

Cf. A017209.

Programs

Magma

[4+9*Floor(n/2): n in [1..60]]; // Bruno Berselli, Sep 18 2013

Mathematica

Table[4 + 9 Floor[n/2], {n, 60}] (* Vincenzo Librandi, Sep 18 2013 *)

PARI

a(n)=n\2*9 + 4 \\ Charles R Greathouse IV, Jul 21 2016

Formula

a(n) = 9*n - a(n-1) - 1, with n > 1, a(1)=4.

G.f.: x*(4 + 9*x - 4*x^2)/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 18 2013

a(n) = a(n-1) + a(n-2) - a(n-3). - Vincenzo Librandi, Sep 18 2013

E.g.f.: (1/4)*(9 - 16*exp(x) + (7 + 18*x)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 21 2016

Extensions

New definition by Vincenzo Librandi Sep 18 2013