A294534 Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n-2) + 2, where a(0) = 1, a(1) = 2, b(0) = 3.

1, 2, 8, 16, 31, 55, 95, 161, 268, 442, 724, 1181, 1921, 3119, 5059, 8198, 13278, 21498, 34799, 56321, 91145, 147492, 238664, 386184, 624877, 1011091, 1635999, 2647122, 4283155, 6930312, 11213503, 18143852, 29357393, 47501284, 76858717, 124360042, 201218801

Offset

0,2

Comments

The increasing complementary sequences a() and b() are uniquely determined by the titular equation and initial values. See A294532 for a guide to related sequences. Conjecture: a(n)/a(n-1) -> (1 + sqrt(5))/2 = golden ratio (A001622)..

Links

Table of n, a(n) for n=0..36.

Clark Kimberling, Complementary equations, J. Int. Seq. 19 (2007), 1-13.

Example

a(0) = 1, a(1) = 2, b(0) = 3, so that
b(1) = 4 (least "new number")
a(2)  = a(1) + a(0) + b(0) + 2 = 8
Complement: (b(n)) = (3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, ...)

Mathematica

mex := First[Complement[Range[1, Max[#1] + 1], #1]] &;
a[0] = 1; a[1] = 3; b[0] = 2;
a[n_] := a[n] = a[n - 1] + a[n - 2] + b[n - 2] + 2;
b[n_] := b[n] = mex[Flatten[Table[Join[{a[n]}, {a[i], b[i]}], {i, 0, n - 1}]]];
Table[a[n], {n, 0, 40}]  (* A294534 *)
Table[b[n], {n, 0, 10}]

Crossrefs

Cf. A001622, A294532.

Sequence in context: A077071 A187216 A210729 * A294542 A294553 A295949

Adjacent sequences: A294531 A294532 A294533 * A294535 A294536 A294537

Keyword

nonn,easy

Author

Clark Kimberling, Nov 03 2017

Status

approved