OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (15, -63, 49).
FORMULA
a(1)=1, a(2)=15, a(n) = 14*a(n-1) - 49*a(n-2) + 1. - Vincenzo Librandi, Oct 23 2012
G.f.: x/((1-x)*(1-7*x)^2). - Vincenzo Librandi, Oct 23 2012
a(n) = (1/36)*(1 + 7^n*(6*n-1)). - Vincenzo Librandi, Oct 26 2012
a(1)=1, a(2)=15, a(3)=162, a(n) = 15*a(n-1) - 63*a(n-2) + 49*a(n-3). - Harvey P. Dale, Jun 26 2013
MAPLE
a:=n->sum (7^n-7^j, j=0..n): seq(a(n)/6, n=1..21); # Zerinvary Lajos, Dec 14 2008
MATHEMATICA
CoefficientList[Series[1/((1 - x)(1 - 7*x)^2), {x, 0, 40}], x] (* Vincenzo Librandi, Oct 23 2012 *)
LinearRecurrence[{15, -63, 49}, {1, 15, 162}, 30] (* Harvey P. Dale, Jun 26 2013 *)
PROG
(Magma) I:=[1, 15]; [n le 2 select I[n] else 14*Self(n-1)-49*Self(n-2)+1: n in [1..30]]; // Vincenzo Librandi, Oct 23 2012
(Magma) [(1/36)*(1+7^n*(6*n-1)): n in [1..20]]; // Vincenzo Librandi, Oct 26 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved