OFFSET
1,5
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))) * ([i=k] + [i=n-i-k] - [k=n-i-k]) * (n-i-k), where [] is the Iverson bracket.
Conjectures from Colin Barker, May 15 2019: (Start)
G.f.: x^3*(1 + 2*x^2 + x^3 + 4*x^4 + x^5 + x^6) / ((1 - x)^3*(1 + x)^2*(1 + x^2)^2*(1 + x + x^2)).
a(n) = a(n-3) + 2*a(n-4) - 2*a(n-7) - a(n-8) + a(n-11) for n>11.
(End)
MATHEMATICA
Table[Sum[Sum[(n - i - k) (KroneckerDelta[i, k] + KroneckerDelta[i, n - i - k] - KroneckerDelta[k, n - i - k]) 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