A299405 Solution (a(n)) of the system of 5 complementary equations in Comments.

1, 5, 9, 14, 18, 22, 27, 31, 35, 39, 43, 48, 52, 56, 60, 65, 69, 73, 77, 82, 86, 90, 95, 99, 103, 107, 111, 116, 120, 124, 128, 133, 137, 141, 145, 150, 154, 158, 163, 167, 171, 175, 179, 184, 188, 192, 196, 201, 205, 209, 213, 218, 222, 226, 231, 235, 239

Offset

0,2

Comments

Define sequences a(n), b(n), c(n), d(n) recursively, starting with a(0) = 1, b(0) = 2, c(0) = 3;:

a(n) = least new;

b(n) = least new;

c(n) = least new;

d(n) = least new;

e(n) = a(n) + b(n) + c(n) + d(n);

where "least new k" means the least positive integer not yet placed.

***

Conjecture: for all n >= 0,

0 <= 17n - 11 - 4 a(n) <= 4

0 <= 17n - 7 - 4 b(n) <= 4

0 <= 17n - 3 - 4 c(n) <= 3

0 <= 17n + 1 - 4 d(n) <= 3

0 <= 17n - 5 - e(n) <= 3

***

The sequences a,b,c,d,e partition the positive integers. The sequence e can be called the "anti-tetranacci sequence"; see A075326 (anti-Fibonacci numbers) and A265389 (anti-tribonacci numbers).

Links

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

Example

n:   0  1   2    3   4   5   6   7   8   9
a:   1  5   9   14  18  22  27  31  35  39
b:   2  6   11  15  19  23  28  32  36  40
c:   3  7   12  16  20  24  29  33  37  41
d:   4  8   13  17  21  25  30  34  38  42
e:  10  26  45  62  78  94 114 130 146 162

Mathematica

z = 200;
mex[list_, start_] := (NestWhile[# + 1 &, start, MemberQ[list, #] &]);
a = {1}; b = {2}; c = {3}; d = {4}; e = {}; AppendTo[e,
Last[a] + Last[b] + Last[c] + Last[d]];
Do[{AppendTo[a, mex[Flatten[{a, b, c, d, e}], 1]],
   AppendTo[b, mex[Flatten[{a, b, c, d, e}], 1]],
   AppendTo[c, mex[Flatten[{a, b, c, d, e}], 1]],
   AppendTo[d, mex[Flatten[{a, b, c, d, e}], 1]],
   AppendTo[e, Last[a] + Last[b] + Last[c] + Last[d]]}, {z}];
Take[a, 100]  (* A299405 *)
Take[b, 100]  (* A299637 *)
Take[c, 100]  (* A299638 *)
Take[d, 100]  (* A299641 *)
Take[e, 100]  (* A299409 *)

Crossrefs

Cf. A036554, A299634, A299637, A299638, A299641, A299409.

Sequence in context: A314826 A314827 A314828 * A314829 A287243 A314830

Adjacent sequences: A299402 A299403 A299404 * A299406 A299407 A299408

Keyword

nonn,easy

Author

Clark Kimberling, Apr 22 2018

Status

approved