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 A274776 Irregular triangle read by rows: T(n,k) = number of arrangements of n circles in the affine plane forming k regions, including the regions that do not belong to the circles. 5
 1, 0, 2, 1, 0, 0, 4, 4, 2, 0, 4, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Consider the arrangements of n circles described in A250001. Note that the sum of the 4th row must be equal to A250001(4) = 173. LINKS FORMULA T(n,k) = A274818(n,k)/k. EXAMPLE Triangle begins: 1; 0, 2, 1; 0, 0, 4, 4, 2, 0, 4; 0, 0, 0, ... ... For n = 3 and k = 5 there are 2 arrangements of 3 circles in the affine plane forming 5 regions, including the regions that do not belong to the circles, so T(3,5) = 2. For n = 3 and k = 6 there are no arrangements of 3 circles in the affine plane forming 6 regions, including the regions that do not belong to the circles, so T(3,6) = 0. Of course, there is a right triangle of all zeros starting from the second row. CROSSREFS Sum of n-th row = A250001(n). First differs from A274777 at a(10). Cf. A250001, A249752, A252158, A261070, A274818, A274822. Sequence in context: A121465 A192396 A094449 * A274777 A136129 A278213 Adjacent sequences:  A274773 A274774 A274775 * A274777 A274778 A274779 KEYWORD nonn,tabf,hard,more AUTHOR Omar E. Pol, Jul 06 2016 STATUS approved

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Last modified July 24 15:05 EDT 2021. Contains 346273 sequences. (Running on oeis4.)