

A249752


Triangle read by rows: T(n,k) = number of arrangements of n circles in the affine plane having k outer circles.


7




OFFSET

1,3


COMMENTS

Consider the arrangements of n circles described in A250001.
T(n,k) is the number of arrangements of n circles in the affine plane whose perimeters are formed with parts from k circles.  Omar E. Pol, Aug 09 2015
From Omar E. Pol, Jul 06 2016: (Start)
Observation 1: column 1 gives A250001, at least if 1<=n<=4.
Observation 2: sum of nth row = T(n+1,1), at least if 1<=n<=3. (End)


LINKS

Table of n, a(n) for n=1..10.


EXAMPLE

Triangle begins:
1;
1, 2;
3, 5, 6;
14, 52, 60, 47;
...


CROSSREFS

Sum of nth row = A250001(n).
Leading diagonal gives A274702.
Cf. A252158, A261070, A274776, A274777.
Sequence in context: A253647 A131825 A289124 * A222313 A079226 A055686
Adjacent sequences: A249749 A249750 A249751 * A249753 A249754 A249755


KEYWORD

nonn,tabl,hard,more


AUTHOR

Omar E. Pol, Dec 14 2014


EXTENSIONS

Corrected a(5)a(6) and added a(7)a(10) from Omar E. Pol, Oct 13 2015


STATUS

approved



