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 A285996 Triangle read by rows, 1<=k<=n, T(n,k) = number of arrangements of n circles in the affine plane having k separated islands. 3
 1, 2, 1, 11, 2, 1, 156, 14, 2, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Consider the rules for the arrangements of n circles described in A250001. Note that T(4,1) = 156 includes the arrangement of 4 circles in which there is a little circle that is surrounded by the union of three solid circles, because the little circle is an inland island, or lake island, which does not count. So there is only one separated island. Hence T(4,2) = 14 does not include the mentioned arrangement. Question: is 1 together with the first column of the triangle the same as A275923? LINKS EXAMPLE Triangle begins: 1; 2,   1; 11,  2,  1; 156, 14, 2, 1; CROSSREFS Another version of A252158. Row sums give A250001, n >= 1. Right border gives A000012. Cf. A249752, A275923. Sequence in context: A309497 A281350 A252158 * A191618 A306547 A143888 Adjacent sequences:  A285993 A285994 A285995 * A285997 A285998 A285999 KEYWORD nonn,tabl,hard,more AUTHOR Omar E. Pol, May 21 2017 STATUS approved

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Last modified December 16 04:05 EST 2019. Contains 330013 sequences. (Running on oeis4.)