A106832 4*n-2 and 6*n alternatively.

2, 6, 6, 12, 10, 18, 14, 24, 18, 30, 22, 36, 26, 42, 30, 48, 34, 54, 38, 60, 42, 66, 46, 72, 50, 78, 54, 84, 58, 90, 62, 96, 66, 102, 70, 108, 74, 114, 78, 120, 82, 126, 86, 132, 90, 138, 94, 144, 98, 150

Offset: 1

Author

Zak Seidov, May 19 2005

Keywords

• nonn
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).

Programs

Magma

&cat[[4*n-2,6*n]: n in [1..25]]; // Bruno Berselli, Sep 26 2011

Maple

a:=n->add(2+add((-1)^j, j=2..n),j=1..n):seq(a(n),n=1..69); # Zerinvary Lajos, Dec 13 2008

Mathematica

Flatten[Table[{4n-2,6n},{n,30}]] (* or *) LinearRecurrence[{0,2,0,-1},{2,6,6,12},60] (* Harvey P. Dale, Aug 14 2013 *)

Formula

a(n) = n*(3 - (n mod 2)).

From Bruno Berselli, Sep 26 2011: (Start)

G.f.: 2*x*(1+3*x+x^2)/(1-x^2)^2.

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

a(n) = -a(-n) = A195013(n) - A195013(-n). (End)

a(n) = 2*a(n-2) - a(n-4); a(1)=2, a(2)=6, a(3)=6, a(4)=12. - Harvey P. Dale, Aug 14 2013

Extensions

Definition corrected by Bruno Berselli, Sep 26 2011