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 A052610 E.g.f. 1/(1-x-2x^3). 0
 1, 1, 2, 18, 120, 840, 9360, 115920, 1491840, 22861440, 395539200, 7304774400, 148011494400, 3281639961600, 77850214041600, 1975895970048000, 53666956062720000, 1547595999645696000, 47204701332332544000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 555 FORMULA E.g.f.: -1/(-1+x+2*x^3) Recurrence: {a(1)=1, a(0)=1, a(2)=2, (-12*n^2-22*n-12-2*n^3)*a(n) +(-n-3)*a(n+2) +a(n+3)=0} Sum(1/29*(2+6*_alpha^2+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+2*_Z^3))*n! MAPLE spec := [S, {S=Sequence(Union(Z, Prod(Z, Z, Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A007798 A058052 A119578 * A052653 A289830 A060589 Adjacent sequences:  A052607 A052608 A052609 * A052611 A052612 A052613 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified October 15 01:40 EDT 2019. Contains 328025 sequences. (Running on oeis4.)