|
| |
|
|
A057750
|
|
Number of non-factorable subsets of size >= 2 of a 1 X n uniform grid.
|
|
2
| |
|
|
0, 1, 4, 10, 23, 49, 100, 202, 413, 839, 1713, 3493, 7130, 14535, 29617, 60158, 122077, 247132, 499409, 1007440, 2029801, 4083888, 8208828, 16484742
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,3
|
|
|
COMMENTS
| A set is factorable if it is the union of at least two disjoint translated copies of a subset of at least two elements. E.g. the subset *..*.**..***.*.* of the 1x16 grid (where * denotes gridpoints in the selected subset and . denotes the remaining unselected gridpoints) is factorable into 3 copies of the 3-element subset *..*.*, as shown by displaying the factors by 1..1.12..232.3.3, where the numerals denote the elements of a particular translated copy.
|
|
|
EXAMPLE
| The factorable subsets of (......) are (1122..), (11.22.), (.1122.), (1.12.2), (11..22), (.11.22), (..1122) and (111222) and there are seven subsets with fewer than 2 elements, so a(6)=2^6-8-7=49.
|
|
|
CROSSREFS
| Cf. A057765.
Sequence in context: A084446 A158671 A001980 * A118645 A200759 A137531
Adjacent sequences: A057747 A057748 A057749 * A057751 A057752 A057753
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| John W. Layman (layman(AT)math.vt.edu), Oct 30 2000
|
| |
|
|
