A168411 a(n) = 7 + 9*floor((n-1)/2).

7, 7, 16, 16, 25, 25, 34, 34, 43, 43, 52, 52, 61, 61, 70, 70, 79, 79, 88, 88, 97, 97, 106, 106, 115, 115, 124, 124, 133, 133, 142, 142, 151, 151, 160, 160, 169, 169, 178, 178, 187, 187, 196, 196, 205, 205, 214, 214, 223, 223, 232, 232, 241, 241, 250, 250, 259

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. A017245.

Programs

Magma

[7+9*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi, Sep 19 2013

Mathematica

Table[7 + 9 Floor[(n - 1)/2], {n, 70}] (* or *) CoefficientList[Series[(7 + 2 x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)

Formula

a(n) = 9*n - a(n-1) - 4, with n>1, a(1)=7.

G.f.: x*(7 + 2*x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Jul 10 2011

a(n) = a(n-1) +a(n-2) -a(n-3). - Vincenzo Librandi, Sep 19 2013

E.g.f.: (1/4)*(-9 + 8*exp(x) + (18*x + 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 22 2016

Extensions

New definition by Vincenzo Librandi, Sep 19 2013