%I A001559 M3497 N1418
%S A001559 1,4,15,54,193,690,2476,8928,32358,117866,431381,1585842,5853849,
%T A001559 21690378,80650536,300845232,1125555054,4222603968,15881652606,
%U A001559 59873283372,226214536506,856431978324,3248562071800,12344168149224
%N A001559 a(0) = 1, a(1) = 4; thereafter a(n) * (2*n + 10) - a(n-1) * (11*n + 35) 
               + a(n-2) * (8*n + 2) + a(n-3) * (15*n + 7) + a(n-4) * (4*n - 2) = 
               0.
%D A001559 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001559 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001559 Fine, Terrence; Extrapolation when very little is known about the source. 
               Information and Control 16 (1970), 331-359.
%F A001559 0 = -a(n) * n * (2*n + 10) * (7*n + 13) + a(n-1) * (49*n^3 + 252*n^2 
               + 419*n + 240) + a(n-2) * (2*n + 2) * (2*n + 3) * (7*n + 20). - Michael 
               Somos Jul 14 2009
%F A001559 G.f.: 2 / (1 - 4*x + x^2 + 2*x^3 + (1 - 2*x - x^2) * sqrt(1 - 4*x )). 
               - Michael Somos Jul 14 2009
%e A001559 1 + 4*x + 15*x^2 + 54*x^3 + 193*x^4 + 690*x^5 + 2476*x^6 + 8928*x^7 + 
               ...
%o A001559 (PARI) {a(n) = if( n<0, 0, polcoeff( 2 / (1 - 4*x + x^2 + 2*x^3 + (1 
               - 2*x - x^2) * sqrt(1 - 4*x + x*O(x^n))), n))}; /* Michael Somos 
               Jul 14 2009 */
%Y A001559 Sequence in context: A006234 A094821 A071723 this_sequence A002311 A102349 
               A126932
%Y A001559 Adjacent sequences: A001556 A001557 A001558 this_sequence A001560 A001561 
               A001562
%K A001559 nonn
%O A001559 0,2
%A A001559 N. J. A. Sloane (njas(AT)research.att.com).
%E A001559 Better definition and more terms from Michael Somos, Jul 14 2009