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A343370
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a(1) = 1; a(n) = Sum_{d|n, d < n} (-1)^d * a(d).
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3
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1, -1, -1, -2, -1, -1, -1, -4, 0, -1, -1, -4, -1, -1, 1, -8, -1, -2, -1, -4, 1, -1, -1, -12, 0, -1, 0, -4, -1, -3, -1, -16, 1, -1, 1, -10, -1, -1, 1, -12, -1, -3, -1, -4, 0, -1, -1, -32, 0, -2, 1, -4, -1, -4, 1, -12, 1, -1, -1, -16, -1, -1, 0, -32, 1, -3, -1, -4, 1, -3, -1, -36, -1, -1, 0, -4, 1, -3, -1, -32, 0
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OFFSET
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1,4
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LINKS
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FORMULA
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G.f.: x + Sum_{n>=1} (-1)^n * a(n) * x^(2*n) / (1 - x^n).
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MAPLE
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a:= proc(n) option remember; `if`(n<2, 1,
add((-1)^d*a(d), d=numtheory[divisors](n) minus {n}))
end:
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MATHEMATICA
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a[1] = 1; a[n_] := a[n] = Sum[If[d < n, (-1)^d a[d], 0], {d, Divisors[n]}]; Table[a[n], {n, 70}]
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PROG
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(PARI)
memoA343370 = Map();
A343370(n) = if(1==n, 1, my(v); if(mapisdefined(memoA343370, n, &v), v, v = sumdiv(n, d, if(d<n, ((-1)^d)*A343370(d), 0)); mapput(memoA343370, n, v); (v))); \\ Antti Karttunen, Jan 02 2023
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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