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%I #8 Jan 03 2024 05:36:58
%S 0,0,2,3,5,5,16,21,20,16,33,33,44,48,63,84,86,92,103,105,112,130,165,
%T 177,183,173,211,191,214,202,273,302,290,318,359,395,406,422,465,503,
%U 520,508,603,611,623,621,692,728,732,722,719,749,790,832,827,875,876,924,1013,1001
%N Sum of the squarefree numbers less than n that do not divide n.
%F a(n) = Sum_{k=1..n} k * mu(k)^2 * (ceiling(n/k) - floor(n/k)).
%e 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.
%t Table[Sum[k*MoebiusMu[k]^2 (Ceiling[n/k] - Floor[n/k]), {k, n}], {n, 100}]
%o (PARI) a(n) = sum(k=1, n-1, if ((n % k) && issquarefree(k), k)); \\ _Michel Marcus_, Jan 03 2024
%Y Cf. A008683 (mu), A368673.
%K nonn,easy
%O 1,3
%A _Wesley Ivan Hurt_, Jan 02 2024
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