OFFSET
1,7
MATHEMATICA
a[n_]:=a[n]=-1+Sum[Times@@a/@y, {y, Select[IntegerPartitions[n], Length[#]>1&&UnsameQ@@#&]}];
-Array[a, 40]
CROSSREFS
KEYWORD
sign
AUTHOR
Gus Wiseman, Mar 13 2018
STATUS
approved