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A052443
Number of simple unlabeled n-node graphs of connectivity 2.
13
0, 0, 1, 2, 7, 39, 332, 4735, 113176, 4629463, 327695586, 40525166511, 8850388574939, 3453378695335727, 2435485662537561705, 3137225298932374490227, 7448146273273417700880931, 32837456713651735794742705141, 270528237651574516777595556494978, 4186091025846007046878947026003803389
(list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
Jean-François Alcover, Table of n, a(n) for n = 1..23
Jens M. Schmidt, Data files in graph6 format
Eric Weisstein's World of Mathematics, k-Connected Graph.
Gus Wiseman, The a(5) = 7 graphs with vertex-connectivity 2.
FORMULA
a(n) = A002218(n) - A006290(n) for n > 2. - Andrew Howroyd, Sep 04 2019
MATHEMATICA
A002218 = Cases[Import["https://oeis.org/A002218/b002218.txt", "Table"], {_, _}][[All, 2]];
A006290 = Cases[Import["https://oeis.org/A006290/b006290.txt", "Table"], {_, _}][[All, 2]];
a[1] = 0; a[2] = 0; a[3] = 1;
a[n_] := A002218[[n]] - A006290[[n-3]];
Array[a, 23] (* Jean-François Alcover, Jan 07 2021, after Andrew Howroyd *)
CROSSREFS
Column k=2 of A259862.
Cf. A000719, A002218, A006290, A052442, A052444, A052445.
The labeled version is A327198.
2-vertex-connected graphs are A013922.
Cf. A322387, A327051, A327101, A327334.
Sequence in context: A103365 A145086 A367448 * A153744 A266422 A189826
Adjacent sequences: A052440 A052441 A052442 * A052444 A052445 A052446
KEYWORD
nonn
AUTHOR
Eric W. Weisstein
EXTENSIONS
Name clarified and a(8)-a(11) by Jens M. Schmidt, Feb 18 2019
a(2)-a(3) corrected by Andrew Howroyd, Aug 28 2019
a(12)-a(20) from Andrew Howroyd, Sep 04 2019
STATUS
approved

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Last modified November 7 00:13 EST 2024. Contains 377523 sequences.
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