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%I #17 Jan 02 2024 21:54:58
%S 0,0,1,1,1,1,2,3,2,1,2,3,3,2,3,5,4,4,3,5,4,4,4,7,5,4,5,6,5,4,5,8,6,6,
%T 6,11,7,6,7,11,8,7,9,12,10,7,8,13,10,8,7,13,10,10,7,13,10,10,9,14,11,
%U 10,11,15,11,10,11,17,12,12,11,21,13,13,13,19,14,12,14,20,16,12,13,21
%N Number of ways to write n as the sum of two positive distinct squarefree numbers.
%C Number of distinct rectangles with squarefree length and width such that L + W = n, W < L. - _Wesley Ivan Hurt_, Oct 29 2017
%F a(n) = Sum_{k=1..floor((n-1)/2)} mu(k)^2 * mu(n-k)^2. - _Wesley Ivan Hurt_, Oct 26 2017
%p with(numtheory): A098236:=n->add(mobius(i)^2*mobius(n-i)^2, i=1..floor(n/2)-((n+1) mod 2)): seq(A098236(n), n=1..150); # _Wesley Ivan Hurt_, Oct 29 2017
%t Table[Sum[MoebiusMu[i]^2*MoebiusMu[n - i]^2, {i, Floor[(n-1)/2]}], {n, 80}] (* _Wesley Ivan Hurt_, Oct 26 2017 *)
%o (PARI) a(n) = sum(i=1, n\2-(n+1)%2, moebius(i)^2*moebius(n-i)^2); \\ _Michel Marcus_, Oct 27 2017
%Y Cf. A005117, A098235.
%K nonn,easy
%O 1,7
%A _Ralf Stephan_, Aug 31 2004
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