OFFSET
1,1
COMMENTS
LINKS
Paolo Xausa, Table of n, a(n) for n = 1..10000
Index entries for linear recurrences with constant coefficients, signature (2,0,-2,1).
FORMULA
First differences: a(n+1)-a(n) = A142954(n).
From R. J. Mathar, Oct 24 2008: (Start)
a(n) = (n+1)^2-1 = A000466((n+1)/2) if n odd.
a(n) = (n+1)^2-4 = A078371(n/2-1) if n even.
a(n) = 2*a(n-1) -2*a(n-3) +a(n-4).
G.f.: x(3-x+5x^2-3x^3)/((1+x)(1-x)^3). (End)
EXAMPLE
The odd terms of A120070 build the irregular triangle
3;
5;
15,7;
21,9;
35,27,11;
45,33,13;
63,55,39,15;
The leftmost column defines this sequence.
MATHEMATICA
LinearRecurrence[{2, 0, -2, 1}, {3, 5, 15, 21}, 100] (* Paolo Xausa, Dec 05 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Curtz, Sep 26 2008
EXTENSIONS
Edited and extended by R. J. Mathar, Oct 24 2008
STATUS
approved