OFFSET
1,2
FORMULA
a(n) = -Sum_t (-1)^v(t) where the sum is over all same-trees of weight n (see A281145 for definition) and v(t) is the number of nodes (branchings and leaves) in t.
MATHEMATICA
nn=20; -Solve[Table[Sum[a[n/d]^d, {d, Divisors[n]}]==-1, {n, nn}], Array[a, nn]][[1, All, 2]]
CROSSREFS
KEYWORD
sign
AUTHOR
Gus Wiseman, Aug 16 2017
STATUS
approved