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 A076543 Sum(k=1 to n) k*sqf(k); sqf(k)=1 if k is squarefree and sqf(k)=-1 otherwise. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Surprisingly, first 12 terms are also in A074170. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 MATHEMATICA Accumulate[Table[If[SquareFreeQ[n], n, -n], {n, 70}]] (* Harvey P. Dale, Mar 18 2015 *) PROG (PARI) a(n) = sum(k = 1, n, if (issquarefree(k), k, -k)); \\ Michel Marcus, Oct 02 2013 CROSSREFS Cf. A074170. Sequence in context: A125717 A065232 A074170 * A274648 A277558 A005132 Adjacent sequences:  A076540 A076541 A076542 * A076544 A076545 A076546 KEYWORD easy,nonn AUTHOR Zak Seidov, Oct 19 2002 STATUS approved

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