A335987 - OEIS

A335987

Triangular array read by rows: T(n,k) is the number of labeled quasi-orders on [n] that are composed of exactly k irreducible components n>=0, 0<=k<=n.

1, 0, 1, 0, 2, 2, 0, 11, 12, 6, 0, 147, 112, 72, 24, 0, 3412, 1910, 1020, 480, 120, 0, 121553, 52184, 21870, 9600, 3600, 720, 0, 6353629, 2101540, 693672, 254520, 96600, 30240, 5040, 0, 476850636, 120988214, 31163496, 9289728, 3116400, 1048320, 282240, 40320

(list; table; graph; refs; listen; history; text; internal format)

OFFSET

0,5

LINKS

Alois P. Heinz, Rows n = 0..18, flattened

FORMULA

E.g.f.: 1/(1 - y*(1 - 1/A(x))) where A(x) is the e.g.f. for A000798.

EXAMPLE

0, 1;

0, 2, 2;

0, 11, 12, 6;

0, 147, 112, 72, 24;

0, 3412, 1910, 1020, 480, 120;

...

MATHEMATICA

nn = 9; A[x_] := Total[Cases[Import["https://oeis.org/A000798/b000798.txt",

"Table"], {_, _}][[All, 2]]*Table[x^(i - 1)/(i - 1)!, {i, 1, 19}]];

Table[Take[(Range[0, nn]! CoefficientList[Series[1/(1 - y (1 - 1/A[x])), {x, 0, nn}], {x, y}])[[i]], i], {i, 1, nn}] // Grid

CROSSREFS

Cf. A000798 (row sums), A046912 (column k=1), A000142 (main diagonal), A354615.

Sequence in context: A268652 A111810 A019265 * A285539 A285783 A364240

Adjacent sequences: A335984 A335985 A335986 * A335988 A335989 A335990

KEYWORD

nonn,tabl

AUTHOR

Geoffrey Critzer, Jul 10 2022

STATUS

approved