OFFSET
0,3
COMMENTS
All terms are even.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..443 (first 71 terms from Mitchell Keith Bloch)
Mitchell Keith Bloch, Program C++
Mitchell Keith Bloch, Program C++ with Boost
FORMULA
a(n) = Sum_{i=1..p(n)} (n!/(Product_{j=1..n} k(i,j)!) * ((Sum_{j=1..n} k(i,j))^2 - k(i,1))) (where p(n) is the number of partitions A000041 and k(i,j) is the number of partitions of size j in partitioning i).
From Alois P. Heinz, Mar 05 2018: (Start)
E.g.f.: x^2*(2-x)*exp(x/(1-x))/(x-1)^2.
a(n) = (n*(2*n^2-13*n+16)*a(n-1) - n*(n-1)*(n-3)*(n-4)*a(n-2)) / ((n-2)*(n-5))) for n>5. (End)
a(n) ~ n^(n + 3/4) * exp(2*sqrt(n) - n - 1/2) / sqrt(2). - Vaclav Kotesovec, Jun 02 2018
a(n) = n!*( 2*LaguerreL(n-2,1,-1) - LaguerreL(n-3,1,-1) ) for n > 1, with a(0) = a(1) = 0. - G. C. Greubel, Mar 09 2021
EXAMPLE
a(0) = 0 since for 0 lists, 0 conversions are possible.
a(1) = 0 since for the 1 set of 1 list of length 1, there exist no possible conversions.
a(2) = 4 since for the 2 sets of 1 list of length 2, there exists only 1 conversion, and for the 1 set of 2 lists of length 1, there exist 2 conversions.
a(3) = 30 since for the 6 sets of 1 list of length 3, there exists 1 conversion, for the 6 sets of 1 list of length 2 and 1 list of length 1, there exist 3 conversions, and for the 1 set of 3 lists of length 1, there exists 6 conversions.
MAPLE
b:= proc(n, t, c) option remember; `if`(n=0, t^2-c, add(j!*
binomial(n-1, j-1)*b(n-j, t+1, c+`if`(j=1, 1, 0)), j=1..n))
end:
a:= n-> b(n, 0$2):
seq(a(n), n=0..25); # Alois P. Heinz, Mar 05 2018
# second Maple program:
a:= proc(n) option remember; `if`(n<6, [0$2, 4, 30, 240, 2140][n+1],
(n*(2*n^2-13*n+16)*a(n-1)-n*(n-1)*(n-3)*(n-4)*a(n-2))/((n-2)*(n-5)))
end:
seq(a(n), n=0..25); # Alois P. Heinz, Mar 05 2018
MATHEMATICA
(* First program *)
b[n_, t_, c_]:= b[n, t, c]= If[n==0, t^2 -c, Sum[j! Binomial[n-1, j-1]b[n-j, t+1, c + If[j==1, 1, 0]], {j, n}]];
a[n_]:= b[n, 0, 0];
a/@ Range[0, 25] (* Jean-François Alcover, Nov 24 2020, after Alois P. Heinz *)
(* Second program *)
Table[If[n<2, 0, n!*(2*LaguerreL[n-2, 1, -1] -LaguerreL[n-3, 1, -1])], {n, 0, 30}] (* G. C. Greubel, Mar 09 2021 *)
PROG
(Sage) [0, 0, 4]+[factorial(n)*(2*gen_laguerre(n-2, 1, -1) - gen_laguerre(n-3, 0, -1)) for n in (3..30)] # G. C. Greubel, Mar 09 2021
(Magma)
l:= func< n, b | Evaluate(LaguerrePolynomial(n, 1), b) >;
[0, 0, 4]cat[Factorial(n)*( 2*l(n-2, -1) - l(n-3, -1) ): n in [3..30]]; // G. C. Greubel, Mar 09 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Mitchell Keith Bloch, Feb 26 2018
EXTENSIONS
More terms from Mitchell Keith Bloch, Mar 05 2018
STATUS
approved