A293349 Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n-2) + n, where a(0) = 1, a(1) = 3, b(0) = 2, b(1) = 4.

1, 3, 8, 18, 35, 64, 112, 192, 322, 534, 878, 1436, 2340, 3804, 6174, 10010, 16219, 26266, 42524, 68831, 111398, 180274, 291719, 472042, 763812, 1235907, 1999774, 3235738, 5235571, 8471370, 13707004, 22178439, 35885511, 58064020, 93949603, 152013697

Offset: 0

Author

Clark Kimberling, Oct 28 2017

Keywords

• nonn
• easy

Comments

The complementary sequences a() and b() are uniquely determined by the titular equation and initial values. See A293076 for a guide to related sequences.

Conjecture: a(n)/a(n-1) -> (1 + sqrt(5))/2, the golden ratio.

Examples

			a(0) = 1, a(1) = 3, b(0) = 2, b(1) = 4, so that
a(2)  = a(1) + a(0) + b(0) + 2 = 8;
a(3) = a(2) + a(1) + b(1) + 3 = 18.
Complement: (b(n)) = (2, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14,...)
		

Crossrefs

Cf. A001622 (golden ratio), A293076.

Programs

Mathematica

mex := First[Complement[Range[1, Max[#1] + 1], #1]] &;
a[0] = 1; a[1] = 3; b[0] = 2; b[1] = 4;
a[n_] := a[n] = a[n - 1] + a[n - 2] + b[n - 2] + n;
b[n_] := b[n] = mex[Flatten[Table[Join[{a[n]}, {a[i], b[i]}], {i, 0, n - 1}]]];
Table[a[n], {n, 0, 40}]  (* A293349 *)
Table[b[n], {n, 0, 10}]