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A339069 Triangle read by rows: T(n,k) is the number of unlabeled series-reduced 2-connected graphs with n nodes and k edges (n >= 4, ceiling(3*n/2) <= k <= n*(n-1)/2). 3
1, 1, 1, 1, 2, 4, 5, 4, 2, 1, 1, 4, 17, 30, 34, 29, 17, 9, 5, 2, 1, 1, 5, 33, 133, 307, 464, 505, 438, 310, 188, 103, 52, 23, 11, 5, 2, 1, 1, 25, 277, 1352, 3953, 7939, 11897, 14131, 13827, 11465, 8235, 5226, 2966, 1537, 737, 333, 144, 62, 25, 11, 5, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,5

LINKS

Andrew Howroyd, Table of n, a(n) for n = 4..732 (rows n=4..18, extracted from Robinson's tables)

R. W. Robinson, Tables of 2-Connected and 3-Connected Graphs by Nodes and Edges, Table V, pages 10-18.

R. W. Robinson and T. R. S. Walsh, Inversion of cycle index sum relations for 2- and 3-connected graphs, J. Combin. Theory Ser. B. 57 (1993), 289-308.

EXAMPLE

Triangle begins:

===========================================================

n/k | 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

----+------------------------------------------------------

4 | 1;

5 | 1, 1, 1;

6 | 2, 4, 5, 4, 2, 1, 1;

7 | 4, 17, 30, 34, 29, 17, 9, 5, 2, 1, 1;

8 | 5, 33 ...

...

CROSSREFS

Row sums are A006289.

Column sums are A339068.

Cf. A123545, A123546, A339071, A339072.

Sequence in context: A011174 A123545 A123546 * A334422 A317499 A004581

Adjacent sequences: A339066 A339067 A339068 * A339070 A339071 A339072

KEYWORD

nonn,tabf

AUTHOR

Andrew Howroyd, Nov 24 2020

STATUS

approved

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Last modified November 29 13:01 EST 2022. Contains 358429 sequences. (Running on oeis4.)