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A317877 Number of free pure identity multifunctions with one atom and n positions. 8
1, 0, 1, 0, 2, 2, 5, 10, 18, 46, 94, 212, 476, 1058, 2441, 5564, 12880, 29920, 69620, 163220, 383376, 904114, 2139592, 5074784, 12074152, 28789112, 68803148, 164779064, 395373108, 950416330, 2288438591, 5518864858, 13329183894, 32237132814, 78069124640 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
COMMENTS
A free pure identity multifunction (PIM) is either (case 1) the leaf symbol "o", or (case 2) an expression of the form h[g_1, ..., g_k] where h is a PIM, each of the g_i for i = 1, ..., k > 0 is a PIM, and for i != j we have g_i != g_j. The number of positions in a PIM is the number of brackets [...] plus the number of o's.
LINKS
EXAMPLE
The a(8) = 10 PIMs:
o[o[o[o],o]]
o[o[o,o[o]]]
o[o[o[o]],o]
o[o[o][o],o]
o[o,o[o[o]]]
o[o,o[o][o]]
o[o][o[o],o]
o[o][o,o[o]]
o[o[o],o][o]
o[o,o[o]][o]
MATHEMATICA
allIdPMF[n_]:=If[n==1, {"o"}, Join@@Cases[Table[PR[k, n-k-1], {k, n-2}], PR[h_, g_]:>Join@@Table[Apply@@@Tuples[{allIdPMF[h], Select[Tuples[allIdPMF/@p], UnsameQ@@#&]}], {p, Join@@Permutations/@IntegerPartitions[g]}]]];
Table[Length[allIdPMF[n]], {n, 12}]
PROG
(PARI) seq(n)={my(v=vector(n)); v[1]=1; for(n=2, n, my(p=prod(k=1, n, 1 + sum(i=1, n\k, binomial(v[k], i)*x^(i*k)*y^i) + O(x*x^n))); v[n]=sum(k=1, n-2, v[n-k-1]*subst(serlaplace(y^0*polcoef(p, k)), y, 1))); v} \\ Andrew Howroyd, Sep 01 2018
CROSSREFS
Sequence in context: A331540 A329676 A247354 * A075125 A081374 A243338
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 09 2018
EXTENSIONS
Terms a(13) and beyond from Andrew Howroyd, Sep 01 2018
STATUS
approved

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Last modified June 18 10:39 EDT 2024. Contains 373479 sequences. (Running on oeis4.)