OFFSET
0,13
COMMENTS
Also by definition the number of subsets whose sum is one fewer than the product of their complement.
LINKS
Giovanni Resta, Table of n, a(n) for n = 0..2500
EXAMPLE
The initial terms count the following subsets:
0: {}
1: {1}
2: {2}
3: {1,3}
4: {2,3}
7: {4,5}
10: {1,6,7}
12: {7,9}
12: {1,2,4,8}
14: {2,5,9}
14: {1,2,4,11}
15: {1,3,5,7}
16: {3,4,10}
16: {1,3,5,8}
17: {1,10,13}
18: {2,5,15}
19: {11,15}
19: {1,2,6,14}
20: {1,4,6,8}
MATHEMATICA
Table[Length[Select[Subsets[Range[n]], 1+Plus@@#==Times@@Complement[Range[n], #]&]], {n, 0, 10}]
ric[n_, pr_, s_, lst_, t_] := Block[{k}, If[pr == t-s, cnt++]; Do[ If[pr k <= t, ric[n, pr k, s + k, k, t], Break[]], {k, lst+1, n}]]; a[n_] := (cnt = 0; ric[n, 1, 0, 0, n (n + 1)/2 + 1]; cnt); a /@ Range[0, 85] (* Giovanni Resta, Sep 13 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 07 2019
EXTENSIONS
More terms from Alois P. Heinz, Jul 12 2019
STATUS
approved