A294540 Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n-2) + 2*n - 1, where a(0) = 1, a(1) = 2, b(0) = 3.

1, 2, 9, 20, 41, 76, 135, 232, 392, 652, 1075, 1761, 2873, 4674, 7590, 12310, 19949, 32311, 52316, 84686, 137064, 221815, 358947, 580833, 939854, 1520764, 2460698, 3981545, 6442329, 10423963, 16866384, 27290442, 44156924, 71447467, 115604495, 187052069

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..35.

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) + 3 = 9
Complement: (b(n)) = (3, 4, 5, 6, 7, 8, 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] + 2n - 1;
b[n_] := b[n] = mex[Flatten[Table[Join[{a[n]}, {a[i], b[i]}], {i, 0, n - 1}]]];
Table[a[n], {n, 0, 40}]  (* A294540 *)
Table[b[n], {n, 0, 10}]

Crossrefs

Cf. A001622, A294532.

Sequence in context: A373732 A090398 A091941 * A248435 A272211 A259035

Adjacent sequences: A294537 A294538 A294539 * A294541 A294542 A294543

Keyword

nonn,easy

Author

Clark Kimberling, Nov 03 2017

Status

approved