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A076543
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Sum(k=1 to n) k*sqf(k); sqf(k)=1 if k is squarefree and sqf(k)=-1 otherwise.
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1
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1, 3, 6, 2, 7, 13, 20, 12, 3, 13, 24, 12, 25, 39, 54, 38, 55, 37, 56, 36, 57, 79, 102, 78, 53, 79, 52, 24, 53, 83, 114, 82, 115, 149, 184, 148, 185, 223, 262, 222, 263, 305, 348, 304, 259, 305, 352, 304, 255, 205, 256, 204, 257, 203, 258, 202, 259, 317, 376, 316, 377
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OFFSET
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1,2
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COMMENTS
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Surprisingly, first 12 terms are also in A074170.
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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MATHEMATICA
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Accumulate[Table[If[SquareFreeQ[n], n, -n], {n, 70}]] (* Harvey P. Dale, Mar 18 2015 *)
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PROG
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(PARI) a(n) = sum(k = 1, n, if (issquarefree(k), k, -k)); \\ Michel Marcus, Oct 02 2013
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CROSSREFS
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Cf. A074170.
Sequence in context: A125717 A065232 A074170 * A005132 A064388 A064387
Adjacent sequences: A076540 A076541 A076542 * A076544 A076545 A076546
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KEYWORD
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easy,nonn
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AUTHOR
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Zak Seidov, Oct 19 2002
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STATUS
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approved
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