OFFSET
1,7
COMMENTS
Number of distinct rectangles with squarefree length and width such that L + W = n, W < L. - Wesley Ivan Hurt, Oct 29 2017
FORMULA
a(n) = Sum_{k=1..floor((n-1)/2)} mu(k)^2 * mu(n-k)^2. - Wesley Ivan Hurt, Oct 26 2017
MAPLE
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
MATHEMATICA
Table[Sum[MoebiusMu[i]^2*MoebiusMu[n - i]^2, {i, Floor[(n-1)/2]}], {n, 80}] (* Wesley Ivan Hurt, Oct 26 2017 *)
PROG
(PARI) a(n) = sum(i=1, n\2-(n+1)%2, moebius(i)^2*moebius(n-i)^2); \\ Michel Marcus, Oct 27 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Aug 31 2004
STATUS
approved