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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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Last modified May 26 16:52 EDT 2017. Contains 287130 sequences.