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A339070
Triangle read by rows: T(n,k) is the number of unlabeled nonseparable (or 2-connected) graphs with n edges and k nodes (n >= 1, 2 <= k <= n + 1).
9
1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 2, 1, 0, 0, 0, 0, 3, 3, 1, 0, 0, 0, 0, 2, 9, 4, 1, 0, 0, 0, 0, 1, 14, 20, 6, 1, 0, 0, 0, 0, 1, 12, 50, 40, 7, 1, 0, 0, 0, 0, 0, 8, 82, 161, 70, 9, 1, 0, 0, 0, 0, 0, 5, 94, 429, 433, 121, 11, 1, 0, 0, 0, 0, 0, 2, 81, 780, 1729, 1034, 189, 13, 1, 0
OFFSET
1,19
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..325 (rows 1..25, first 18 rows extracted from Robinson's tables, rows 19-20 from Andrew Howroyd)
FORMULA
T(n, n) = 1 for n >= 3.
T(n, n-1) = A253186(n-3) for n >= 3.
EXAMPLE
Triangle T(n,k) begins (n edges >= 1, k vertices >= 2):
1;
0, 0;
0, 1, 0;
0, 0, 1, 0;
0, 0, 1, 1, 0;
0, 0, 1, 2, 1, 0;
0, 0, 0, 3, 3, 1, 0;
0, 0, 0, 2, 9, 4, 1, 0;
0, 0, 0, 1, 14, 20, 6, 1, 0;
0, 0, 0, 1, 12, 50, 40, 7, 1, 0;
0, 0, 0, 0, 8, 82, 161, 70, 9, 1, 0;
0, 0, 0, 0, 5, 94, 429, 433, 121, 11, 1, 0;
...
CROSSREFS
Row sums are A010355.
Column sums are A002218.
Cf. A054923, A123534, A253186, A339071 (transpose), A339160.
Sequence in context: A037856 A037874 A343870 * A352553 A077655 A117886
KEYWORD
nonn,tabl
AUTHOR
Andrew Howroyd, Nov 23 2020
EXTENSIONS
First row and column removed by Andrew Howroyd, Dec 05 2020
STATUS
approved