The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A274777 Irregular triangle read by rows: T(n,k) = number of arrangements of n circles in the affine plane forming k regions, excluding the regions that do not belong to the circles. 5
 1, 0, 2, 1, 0, 0, 4, 4, 2, 1, 3, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS In other words: not counting the regions between circles. 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) = A274819(n,k)/k. EXAMPLE Triangle begins: 1; 0, 2, 1; 0, 0, 4, 4, 2, 1, 3; 0, 0, 0, ... ... For n = 3 and k = 5 there are 2 arrangements of 3 circles in the affine plane forming 5 regions, excluding the regions that do not belong to the circles, so T(3,5) = 2. For n = 3 and k = 6 there is only one arrangement of 3 circles in the affine plane forming 6 regions, excluding the regions that do not belong to the circles, so T(3,6) = 1. 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 A274776 at a(10). Cf. A250001, A249752, A252158, A261070, A274819, A274823. Sequence in context: A192396 A094449 A274776 * A136129 A278213 A034093 Adjacent sequences:  A274774 A274775 A274776 * A274778 A274779 A274780 KEYWORD nonn,tabf,hard,more AUTHOR Omar E. Pol, Jul 06 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 27 17:05 EDT 2021. Contains 346308 sequences. (Running on oeis4.)