OFFSET
1,2
FORMULA
a(n) = 2 * Sum_{i=1..n} (n - i) * mu(2*n - i)^2, where mu is the Möbius function (A008683).
MATHEMATICA
Table[2*Sum[(n - i) MoebiusMu[2 n - i]^2, {i, n}], {n, 80}]
Table[Total[#[[1]]-#[[2]]&/@Select[IntegerPartitions[2n, {2}], SquareFreeQ[ #[[1]]]&]], {n, 60}] (* Harvey P. Dale, Jan 19 2021 *)
PROG
(PARI) a(n) = 2*sum(i=1, n, (n-i)*moebius(2*n-i)^2); \\ Michel Marcus, Nov 08 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Oct 22 2017
STATUS
approved