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A360880
Triangle read by rows: T(n,k) is the number of unlabeled nonseparable (or 2-connected) multigraphs with n edges and k nodes, loops allowed, n >= 1, 2 <= k <= n + 1.
2
1, 2, 0, 4, 1, 0, 6, 2, 1, 0, 9, 6, 3, 1, 0, 12, 14, 13, 4, 1, 0, 16, 28, 39, 22, 5, 1, 0, 20, 52, 112, 98, 39, 6, 1, 0, 25, 93, 281, 383, 236, 63, 8, 1, 0, 30, 152, 655, 1304, 1220, 515, 102, 9, 1, 0, 36, 242, 1408, 3980, 5418, 3512, 1077, 153, 11, 1, 0
OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..190 (rows 1..19)
EXAMPLE
Triangle T(n,k) begins (n edges >= 1, k vertices >= 2):
1;
2, 0;
4, 1, 0;
6, 2, 1, 0;
9, 6, 3, 1, 0;
12, 14, 13, 4, 1, 0;
16, 28, 39, 22, 5, 1, 0;
20, 52, 112, 98, 39, 6, 1, 0;
25, 93, 281, 383, 236, 63, 8, 1, 0;
30, 152, 655, 1304, 1220, 515, 102, 9, 1, 0;
...
CROSSREFS
Columns k=2..3 are A002620(n+1), A050531(n-3).
Row sums are A360881.
Sequence in context: A226949 A166589 A332696 * A255330 A291940 A153345
KEYWORD
nonn,tabl
AUTHOR
Andrew Howroyd, Feb 25 2023
STATUS
approved