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A300864
Signed recurrence over strict trees: a(n) = -1 + Sum_{y1 + ... + yk = n, y1 > ... > yk > 0, k > 1} a(y1) * ... * a(yk).
4
1, 1, 0, 1, 0, 0, 2, -1, 0, 4, -6, 6, 6, -24, 38, -17, -64, 188, -230, -6, 662, -1432, 1286, 1210, -6362, 10692, -5530, -18274, 57022, -74364, 174, 216703, -489544, 467860, 391258, -2256430, 3948206, -2234064, -6725362, 21920402, -29716570, 2095564, 84595798, -198418242, 197499846
OFFSET
1,7
MATHEMATICA
a[n_]:=a[n]=-1+Sum[Times@@a/@y, {y, Select[IntegerPartitions[n], Length[#]>1&&UnsameQ@@#&]}];
-Array[a, 40]
KEYWORD
sign
AUTHOR
Gus Wiseman, Mar 13 2018
STATUS
approved