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A156017 Schroeder paths with two rise colors and two level colors. 3
1, 4, 24, 176, 1440, 12608, 115584, 1095424, 10646016, 105522176, 1062623232, 10840977408, 111811534848, 1163909087232, 12212421230592, 129027376349184, 1371482141884416, 14656212306231296, 157369985643577344, 1696975718802522112, 18369603773021552640 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

G.f.: (1-2x-sqrt(1-12x+4x^2))/(4x);

G.f.: 1/(1-2x-2x/(1-2x-2x/(1-2x-2x/(1-... (continued fraction);

a(n) = 2^n*Sum{k=0..n} C(n+k,2k)*A000108(k) = 2^n*A006318(n).

Hankel transform is 8^C(n+1,2). - Philippe Deléham, Feb 04 2009

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

F. Chapoton, F. Hivert, J.-C. Novelli, A set-operad of formal fractions and dendriform-like sub-operads, arXiv preprint arXiv:1307.0092 [math.CO], 2013.

FORMULA

Conjecture: (n+1)*a(n) +6*(1-2*n)*a(n-1) +4*(n-2)*a(n-2)=0. - R. J. Mathar, Nov 14 2011

a(n) = Sum_{0<=k<=n} A090181(n,k)*2^(n+k). - Philippe Deléham, Nov 27 2011

a(n) ~ sqrt(4+3*sqrt(2))*(6+4*sqrt(2))^n/(2*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Oct 20 2012

G.f.: 1/Q(0) where Q(k) = 1 + k*(1-2*x) - 2*x - 2*x*(k+1)*(k+2)/Q(k+1) ; (continued fraction). - Sergei N. Gladkovskii, Mar 14 2013

MAPLE

A156017_list := proc(n) local j, a, w; a := array(0..n); a[0] := 1;

for w from 1 to n do a[w] := 2*(a[w-1]+add(a[j]*a[w-j-1], j=0..w-1)) od;

convert(a, list) end: A156017_list(20); # Peter Luschny, Feb 29 2016

MATHEMATICA

CoefficientList[Series[(1-2*x-Sqrt[1-12*x+4*x^2])/(4*x), {x, 0, 20}], x] (* Vaclav Kotesovec, Oct 20 2012 *)

CROSSREFS

Sequence in context: A032349 A215709 A103334 * A000309 A112914 A007846

Adjacent sequences:  A156014 A156015 A156016 * A156018 A156019 A156020

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Feb 01 2009

EXTENSIONS

Spelling/notation corrections by Charles R Greathouse IV, Mar 18 2010

STATUS

approved

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Last modified September 30 06:50 EDT 2016. Contains 276618 sequences.