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A278427 Triangle read by rows: CU(n,k) is the number of unlabeled subgraphs with k edges of the n-cycle C_n. 2
1, 1, 1, 2, 1, 1, 3, 2, 1, 1, 4, 3, 3, 1, 1, 5, 4, 5, 3, 1, 1, 6, 5, 7, 6, 4, 1, 1, 7, 6, 9, 9, 8, 4, 1, 1, 8, 7, 11, 12, 13, 9, 5, 1, 1, 9, 8, 13, 15, 18, 15, 12, 5, 1, 1, 10, 9, 15, 18, 23, 22, 21, 13, 6, 1, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

For row n = 3 of the triangle below: there are 3 unlabeled subgraphs of the triangle C_3 with 0 edges, 2 with 1 edge, 1 with 2 edges, and 1 with 3 edges (C_3 itself).

LINKS

Table of n, a(n) for n=1..66.

EXAMPLE

Triangle begins:

   1;

   1,  1;

   2,  1,  1;

   3,  2,  1,  1;

   4,  3,  3,  1,  1;

   5,  4,  5,  3,  1,  1;

   6,  5,  7,  6,  4,  1,  1;

   7,  6,  9,  9,  8,  4,  1,  1;

   8,  7, 11, 12, 13,  9,  5,  1,  1;

   9,  8, 13, 15, 18, 15, 12,  5,  1,  1;

  10,  9, 15, 18, 23, 22, 21, 13,  6,  1,  1;

  ...

CROSSREFS

Rows sums give A000070.

Middle diagonal gives A058397.

Sequence in context: A136575 A193592 A243714 * A077592 A194005 A055794

Adjacent sequences:  A278424 A278425 A278426 * A278428 A278429 A278430

KEYWORD

nonn,more,tabl

AUTHOR

John P. McSorley, Nov 21 2016

STATUS

approved

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Last modified March 18 22:11 EDT 2019. Contains 321305 sequences. (Running on oeis4.)