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A316441 a(n) = Sum (-1)^k where the sum is over all factorizations of n into factors > 1 and k is the number of factors. 21
1, -1, -1, 0, -1, 0, -1, -1, 0, 0, -1, 0, -1, 0, 0, 1, -1, 0, -1, 0, 0, 0, -1, 1, 0, 0, -1, 0, -1, 1, -1, -1, 0, 0, 0, 1, -1, 0, 0, 1, -1, 1, -1, 0, 0, 0, -1, 0, 0, 0, 0, 0, -1, 1, 0, 1, 0, 0, -1, 1, -1, 0, 0, 1, 0, 1, -1, 0, 0, 1, -1, 0, -1, 0, 0, 0, 0, 1, -1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,256

COMMENTS

First term greater than 1 in absolute value is a(256) = 2.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for sequences computed from exponents in factorization of n

FORMULA

Dirichlet g.f.: Product_{n > 1} 1/(1 + 1/n^s).

EXAMPLE

The factorizations of 24 are (2*2*2*3), (2*2*6), (2*3*4), (2*12), (3*8), (4*6), (24); so a(24) = 1 - 2 + 3 - 1 = 1.

MATHEMATICA

facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];

Table[Sum[(-1)^Length[f], {f, facs[n]}], {n, 200}]

PROG

(PARI) A316441(n, m=n, k=0) = if(1==n, (-1)^k, my(s=0); fordiv(n, d, if((d>1)&&(d<=m), s += A316441(n/d, d, k+1))); (s)); \\ Antti Karttunen, Sep 08 2018, after Michael B. Porter's code for A001055

CROSSREFS

Cf. A001222, A001055, A045778, A114592, A162247, A190938, A259936, A281116, A303386.

Sequence in context: A266591 A132194 A174897 * A190938 A342653 A189166

Adjacent sequences:  A316438 A316439 A316440 * A316442 A316443 A316444

KEYWORD

sign

AUTHOR

Gus Wiseman, Jul 03 2018

EXTENSIONS

Secondary offset added by Antti Karttunen, Sep 08 2018

STATUS

approved

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Last modified August 3 19:54 EDT 2021. Contains 346441 sequences. (Running on oeis4.)