A294480 - OEIS

A294480

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

1, 3, 9, 14, 23, 31, 43, 55, 70, 85, 103, 122, 143, 165, 189, 214, 241, 269, 299, 331, 364, 399, 435, 473, 512, 553, 596, 640, 686, 733, 782, 832, 884, 937, 992, 1048, 1106, 1166, 1227, 1290, 1354, 1420, 1487, 1556, 1626, 1698, 1771, 1846, 1923, 2001, 2081

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OFFSET

0,2

COMMENTS

The complementary sequences a() and b() are uniquely determined by the titular equation and initial values. See A294476 for a guide to related sequences.

LINKS

Clark Kimberling, Table of n, a(n) for n = 0..1000

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

EXAMPLE

a(0) = 1, a(1) = 3, b(0) = 2, b(1) = 4, so that

a(2) = a(0) + b(1) = 9

Complement: (b(n)) = (2, 4, 5, 6, 7, 8, 10, 12, 13, 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 - 2] + b[n - 1] + 2n;

b[n_] := b[n] = mex[Flatten[Table[Join[{a[n]}, {a[i], b[i]}], {i, 0, n - 1}]]];