A370167 - OEIS

A370167

Irregular triangle read by rows where T(n,k) is the number of unlabeled simple graphs covering n vertices with k = 0..binomial(n,2) edges.

1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 2, 2, 1, 1, 0, 0, 0, 1, 4, 5, 5, 4, 2, 1, 1, 0, 0, 0, 1, 3, 9, 15, 20, 22, 20, 14, 9, 5, 2, 1, 1, 0, 0, 0, 0, 1, 6, 20, 41, 73, 110, 133, 139, 126, 95, 64, 40, 21, 10, 5, 2, 1, 1, 0, 0, 0, 0, 1, 3, 15, 50, 124, 271, 515, 832, 1181, 1460, 1581, 1516, 1291, 970, 658, 400, 220, 114, 56, 24, 11, 5, 2, 1, 1

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

OFFSET

0,12

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..1350 (rows 0..20)

EXAMPLE

Triangle begins:

0 1

0 0 1 1

0 0 1 2 2 1 1

0 0 0 1 4 5 5 4 2 1 1

0 0 0 1 3 9 15 20 22 20 14 9 5 2 1 1

MATHEMATICA

brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{(Union@@m)[[i]], p[[i]]}, {i, Length[p]}])], {p, Permutations[Range[Length[Union@@m]]]}]]];

Table[Length[Union[brute /@ Select[Subsets[Subsets[Range[n], {2}], {k}], Union@@#==Range[n]&]]], {n, 0, 5}, {k, 0, Binomial[n, 2]}]

PROG

(PARI) \\ G(n) defined in A008406.

row(n)={Vecrev(G(n)-if(n>0, G(n-1)), binomial(n, 2)+1)}

{ for(n=0, 7, print(row(n))) } \\ Andrew Howroyd, Feb 19 2024

CROSSREFS

Column sums are A000664.

Row sums are A002494.

This is the covering case of A008406, labeled A084546.

The labeled version is A054548, row sums A006129, column sums A121251.

The connected case is A054924, row sums A001349, column sums A002905.

The labeled connected case is A062734, with loops A369195.

The connected case with loops is A283755, row sums A054921.

The labeled version w/ loops is A369199, row sums A322661, col sums A173219.

Cf. A000666, A006125, A006649, A054547, A066383, A322700.

Sequence in context: A246271 A049334 A054924 * A046751 A124478 A030353

Adjacent sequences: A370164 A370165 A370166 * A370168 A370169 A370170

KEYWORD

nonn,tabf

AUTHOR

Gus Wiseman, Feb 15 2024

EXTENSIONS

a(42) onwards from Andrew Howroyd, Feb 19 2024

STATUS

approved