OFFSET
4,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 4..445
J. Riordan, Enumeration of trees by height and diameter, IBM J. Res. Dev. 4 (1960), 473-478.
FORMULA
a(n) = A034865(n), n > 4. - R. J. Mathar, Oct 20 2008
(-n+5)*a(n) + n*(n-4)*a(n-1) = 0. - R. J. Mathar, Apr 03 2017
E.g.f.: x^4*(1 + x + x^2)/(6*(1 - x)^2). - G. C. Greubel, Feb 16 2018
MAPLE
[4, seq(factorial(n)*(n-4)/2, n=5..20)]; # Muniru A Asiru, Feb 17 2018
MATHEMATICA
Join[{4}, Table[n!*(n-4)/2, {n, 5, 30}]] (* or *) Drop[With[{nn = 30}, CoefficientList[Series[x^4*(1 + x + x^2)/(6*(1 - x)^2), {x, 0, nn}], x]*Range[0, nn]!], 4] (* G. C. Greubel, Feb 16 2018 *)
PROG
(PARI) x='x+O('x^30); Vec(serlaplace(x^4*(1+x+x^2)/(6*(1-x)^2))) \\ G. C. Greubel, Feb 16 2018
(Magma) [4] cat [Factorial(n)*(n-4)/2: n in [5..30]]; // G. C. Greubel, Feb 16 2018
(GAP) A034866:=Concatenation([4], List([5..20], n->Factorial(n)*(n-4)/2)); # Muniru A Asiru, Feb 17 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved