OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..75
MATHEMATICA
a[0 | 1, 0 | 1] = 0; a[0 | 1, _] = a[_, 0 | 1] = 1; a[i_, j_]:= Module[{slopes, cnt}, slopes = Union@Flatten@Table[(k - j)/(h - i), {h, 0, i - 1}, {k, 0, j - 1}]; cnt[slope_] := Count[Flatten[Table[{h, k}, {h, 0, i - 1}, {k, 0, j - 1}], 1], {h_, k_} /; (k - j)/(h - i) == slope]; Count[cnt /@ slopes, c_ /; c >= 2] + 2]; Table[Sum[(-1)^k*a[k, n - k], {k, 0, n}], {n, 0, 25}] (* G. C. Greubel, Dec 07 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Terms a(42) onward added by G. C. Greubel, Dec 07 2017
STATUS
approved