OFFSET
0,2
COMMENTS
Central coefficients of number triangle A115284.
LINKS
FORMULA
G.f.: (1+8*x+7*x^2)/(1-x)^2.
a(n) = 7*0^n + 2*(8*n-3).
a(n) = sum{k=0..n, (4-C(1, k)-2*C(0, k))^2}.
a(n) = A115284(2n, n).
a(0)=1, a(1)=10, a(2)=26, a(n) = 2*a(n-1)-a(n-2). [Harvey P. Dale, Aug 19 2011]
MATHEMATICA
Accumulate[CoefficientList[Series[(1+x)^2/(1-x), {x, 0, 110}], x]^2] (* or *) Join[{1}, LinearRecurrence[{2, -1}, {10, 26}, 110]] (* Harvey P. Dale, Aug 19 2011 *)
PROG
(PARI) Vec((1+8*x+7*x^2)/(1-x)^2 + O(x^80)) \\ Michel Marcus, Feb 12 2016
(Magma) I:=[1, 10, 26]; [n le 3 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..60]]; // Vincenzo Librandi, Feb 12 2016
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jan 19 2006
STATUS
approved