OFFSET
1,2
COMMENTS
Inverse weigh transform of A000005.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..2500
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
add(binomial(a(i), j)*b(n-i*j, i-1), j=0..n/i)))
end:
a:= proc(n) option remember; numtheory[tau](n)-b(n, n-1) end:
seq(a(n), n=1..80); # Alois P. Heinz, Oct 27 2019
MATHEMATICA
b[n_, i_] := b[n, i] = If[n == 0, 1, If[i < 1, 0, Sum[Binomial[a[i], j] b[n - i j, i - 1], {j, 0, n/i}]]]; a[n_] := a[n] = DivisorSigma[0, n] - b[n, n - 1]; Array[a, 65]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Oct 27 2019
STATUS
approved