A168328 a(n) = 6 * floor( n/2 ).

0, 6, 6, 12, 12, 18, 18, 24, 24, 30, 30, 36, 36, 42, 42, 48, 48, 54, 54, 60, 60, 66, 66, 72, 72, 78, 78, 84, 84, 90, 90, 96, 96, 102, 102, 108, 108, 114, 114, 120, 120, 126, 126, 132, 132, 138, 138, 144, 144, 150, 150, 156, 156, 162, 162, 168, 168, 174, 174, 180, 180

Offset: 1

Author

Vincenzo Librandi, Nov 23 2009

Keywords

• nonn
• easy
• less

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. A004526, A008588.

Programs

Magma

[n eq 1 select 0 else 6*n-Self(n-1)-6: n in [1..70]]; // Vincenzo Librandi, Sep 17 2013

Mathematica

Table[6 Floor[n/2], {n, 70}] (* Bruno Berselli, Sep 18 2013 *)

Formula

a(n) = 6*n - a(n-1) - 6 for n>1, a(1)=0.

G.f.: 6*x^2/((1+x)*(1-x)^2). - Bruno Berselli, Sep 17 2013

a(n) = 6*A004526(n). Bruno Berselli, Sep 17 2013

E.g.f.: 3*(x*cosh(x) + (x - 1)*sinh(x)). - G. C. Greubel, Jul 18 2016

Extensions

G.f. adapted to the offset by Vincenzo Librandi, Sep 17 2013

New definition by Bruno Berselli, Sep 18 2013