A019992 a(n) = 4*a(n-1) + a(n-2) - a(n-3) - a(n-5).

5, 21, 88, 368, 1538, 6427, 26857, 112229, 468978, 1959746, 8189306, 34221135, 143001871, 597570335, 2497102330, 10434788478, 43604464772, 182212543365, 761422279419, 3181800093939, 13295975323332, 55560674643076, 232174661258332, 970201922073653, 4054239874815929, 16941690784755705, 70795240417122020

Offset: 0

Author

R. K. Guy

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (4,1,-1,0,-1).

Crossrefs

This is different from A010925. See the comments in that sequence.

Programs

Magma

I:=[5, 21, 88, 368, 1538]; [n le 5 select I[n] else 4*Self(n-1)+Self(n-2)-Self(n-3)-Self(n-5): n in [1..30]]; // Vincenzo Librandi, Apr 20 2012

Mathematica

CoefficientList[Series[(5+x-x^2-x^4)/(1-4*x-x^2+x^3+x^5),{x,0,30}],x] (* Vincenzo Librandi, Apr 20 2012 *)
LinearRecurrence[{4,1,-1,0,-1},{5,21,88,368,1538},30] (* Harvey P. Dale, May 03 2020 *)

Formula

G.f.: (5+x-x^2-x^4)/(1-4*x-x^2+x^3+x^5). - Colin Barker, Feb 21 2012

Extensions

More terms from Pab Ter (pabrlos(AT)yahoo.com), May 23 2004