login
A326441
Number of subsets of {1..n} whose sum is equal to the product of their complement.
6
0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 3, 1, 2, 1, 3, 3, 3, 3, 1, 4, 4, 3, 2, 2, 4, 3, 5, 3, 2, 4, 5, 4, 5, 6, 1, 4, 2, 5, 4, 7, 4, 4, 3, 3, 6, 14, 3, 4, 10, 6, 3, 6, 4, 4, 4, 8, 7, 6, 8, 7, 10, 5, 11, 8, 5, 11, 4, 7, 7, 5, 8, 12, 5, 6, 9, 8, 11, 8, 5, 8, 9, 8, 10, 8
OFFSET
0,11
COMMENTS
Essentially the same as A178830. - R. J. Mathar, Jul 12 2019
LINKS
EXAMPLE
The initial terms count the following subsets:
1: {1}
3: {1,2}
5: {3,5}
6: {3,4,5}
7: {2,4,5,7}
8: {2,4,5,6,7}
9: {2,3,5,6,7,9}
10: {4,5,6,8,9,10}
10: {2,3,5,6,7,8,9}
10: {1,2,3,4,5,8,9,10}
Also the number of subsets of {1..n} whose product is equal to the sum of their complement. For example, the initial terms count the following subsets:
1: {}
3: {3}
5: {1,2,4}
6: {1,2,6}
7: {1,3,6}
8: {1,3,8}
9: {1,4,8}
10: {6,7}
10: {1,4,10}
10: {1,2,3,7}
MAPLE
b:= proc(n, s, p)
`if`(s=p, 1, `if`(n<1, 0, b(n-1, s, p)+
`if`(s-n<p*n, 0, b(n-1, s-n, p*n))))
end:
a:= n-> b(n, n*(n+1)/2, 1):
seq(a(n), n=0..100); # Alois P. Heinz, Jul 12 2019
MATHEMATICA
Table[Length[Select[Subsets[Range[n]], Plus@@#==Times@@Complement[Range[n], #]&]], {n, 0, 10}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 07 2019
EXTENSIONS
a(21)-a(83) from Giovanni Resta, Jul 08 2019
STATUS
approved