A049641 a(n) = Sum_{i=0..n} ((-1)^i)*T(i,n-i), array T as in A049639.

0, 0, 2, 0, 3, 0, 5, 0, 7, 0, 11, 0, 13, 0, 19, 0, 23, 0, 29, 0, 33, 0, 43, 0, 47, 0, 59, 0, 65, 0, 73, 0, 81, 0, 97, 0, 103, 0, 121, 0, 129, 0, 141, 0, 151, 0, 173, 0, 181, 0, 201, 0, 213, 0, 231, 0, 243, 0, 271, 0, 279, 0, 309, 0, 325, 0, 345, 0, 361, 0, 385

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

Cf. A005728, A049643.

Sequence in context: A320311 A240140 A240141 * A240142 A240143 A240144

Adjacent sequences: A049638 A049639 A049640 * A049642 A049643 A049644

Keyword

nonn

Author

Clark Kimberling

Extensions

Terms a(42) onward added by G. C. Greubel, Dec 07 2017

Status

approved