login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A274819 Triangle read by rows: T(n,k) = total number of regions in all arrangements of n circles in the affine plane forming k regions, excluding the regions that do not belong to the circles. 4
1, 0, 4, 3, 0, 0, 12, 16, 10, 6, 21, 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.

LINKS

Table of n, a(n) for n=1..14.

FORMULA

T(n,k) = k*A274777(n,k).

EXAMPLE

Triangle begins:

1;

0, 4,  3;

0, 0, 12, 16, 10, 6, 21;

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*5 = 10.

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*6 = 6.

Of course, there is a right triangle of all zeros starting from the second row.

CROSSREFS

Row sums give A274823(n).

First differs from A274818 at a(10).

Cf. A250001, A274777.

Sequence in context: A019984 A187765 A274818 * A106646 A056969 A131106

Adjacent sequences:  A274816 A274817 A274818 * A274820 A274821 A274822

KEYWORD

nonn,tabf,hard,more

AUTHOR

Omar E. Pol, Jul 07 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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 6 06:34 EST 2019. Contains 329784 sequences. (Running on oeis4.)