OFFSET
1,6
LINKS
Wikipedia, Integer Triangle
FORMULA
a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} sign(floor((i+k)/(n-i-k+1))) * mu(i)^2 * mu(k)^2 * mu(n-i-k)^2 * k, where mu is the Möbius function (A008683).
MATHEMATICA
Table[Sum[Sum[k*MoebiusMu[i]^2*MoebiusMu[k]^2*MoebiusMu[n - k - i]^2*Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, May 14 2019
STATUS
approved