A168398 a(n) = 4 + 8*floor((n-1)/2).

4, 4, 12, 12, 20, 20, 28, 28, 36, 36, 44, 44, 52, 52, 60, 60, 68, 68, 76, 76, 84, 84, 92, 92, 100, 100, 108, 108, 116, 116, 124, 124, 132, 132, 140, 140, 148, 148, 156, 156, 164, 164, 172, 172, 180, 180, 188, 188, 196, 196, 204, 204, 212, 212, 220, 220, 228, 228

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Formula

a(n) = 8*n - a(n-1) - 8, with n>1, a(1)=4.

G.f.: 4*x*(1 + 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

a(n) = 4 * A109613(n-1). - Bruno Berselli, Sep 18 2013

E.g.f.: 4*(1 + (x - 1)*cosh(x) + x*sinh(x)). - G. C. Greubel, Jul 20 2016

Mathematica

Table[4 + 8*Floor[(n - 1)/2], {n, 60}] (* Vincenzo Librandi, Sep 18 2013 *)
LinearRecurrence[{1, 1, -1}, {4, 4, 12}, 60] (* or *) With[{r=NestList[ #+8&, 4, 30]}, Riffle[r, r]] (* Harvey P. Dale, Oct 18 2021 *)

Prog

(Magma) [4+8*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi, Sep 18 2013

Crossrefs

Cf. A017113, A109613.

Sequence in context: A273412 A206488 A273491 * A281913 A178776 A282503

Adjacent sequences: A168395 A168396 A168397 * A168399 A168400 A168401

Keyword

nonn,easy,less

Author

Vincenzo Librandi, Nov 25 2009

Extensions

New definition by Vincenzo Librandi, Sep 18 2013

Status

approved