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 A368674 Sum of the squarefree numbers less than n that do not divide n. 1
 0, 0, 2, 3, 5, 5, 16, 21, 20, 16, 33, 33, 44, 48, 63, 84, 86, 92, 103, 105, 112, 130, 165, 177, 183, 173, 211, 191, 214, 202, 273, 302, 290, 318, 359, 395, 406, 422, 465, 503, 520, 508, 603, 611, 623, 621, 692, 728, 732, 722, 719, 749, 790, 832, 827, 875, 876, 924, 1013, 1001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..60. FORMULA a(n) = Sum_{k=1..n} k * mu(k)^2 * (ceiling(n/k) - floor(n/k)). EXAMPLE a(12) = 33. There are 4 squarefree numbers less than 12 that do not divide 12, namely: 5, 7, 10, and 11. Their sum is 5 + 7 + 10 + 11 = 33. MATHEMATICA Table[Sum[k*MoebiusMu[k]^2 (Ceiling[n/k] - Floor[n/k]), {k, n}], {n, 100}] PROG (PARI) a(n) = sum(k=1, n-1, if ((n % k) && issquarefree(k), k)); \\ Michel Marcus, Jan 03 2024 CROSSREFS Cf. A008683 (mu), A368673. Sequence in context: A342437 A079022 A368706 * A095296 A256301 A226609 Adjacent sequences: A368671 A368672 A368673 * A368675 A368676 A368677 KEYWORD nonn,easy AUTHOR Wesley Ivan Hurt, Jan 02 2024 STATUS approved

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Last modified April 12 10:51 EDT 2024. Contains 371632 sequences. (Running on oeis4.)