A356220 a(n) = A108598(A001950(n)).

3, 9, 12, 18, 23, 27, 32, 36, 41, 47, 50, 56, 61, 65, 70, 74, 79, 85, 88, 94, 97, 103, 108, 112, 117, 123, 126, 132, 135, 141, 146, 150, 155, 161, 164, 170, 173, 179, 184, 188, 193, 197, 202, 208, 211, 217, 222, 226, 231, 235, 240, 246, 249, 255, 258, 264

Offset

1,1

Comments

This is the fourth of four sequences that partition the positive integers. Suppose that u = (u(n)) and v = (v(n)) are increasing sequences of positive integers. Let u' and v' be their (increasing) complements, and consider these four sequences:

(1) v o u, defined by (v o u)(n) = v(u(n));

(2) u o v';

(3) v o u';

(4) v' o u'.

Every positive integer is in exactly one of the four sequences. For the reverse composites, u o v, u o v', u' o v, u' o v', see A356104 to A356107.

Assume that if w is any of the sequences u, v, u', v', then lim_{n->oo} w(n)/n exists and defines the (limiting) density of w. For w = u,v,u',v', denote the densities by r,s,r',s'. Then the densities of sequences (1)-(4) exist, and

1/(r*r') + 1/(r*s') + 1/(s*s') + 1/(s*r') = 1.

For A356220, u, v, u', v', are the Beatty sequences given by u(n) = floor(n*(1+sqrt(5))/2) and v(n) = floor(n*sqrt(5)), so r = (1+sqrt(5))/2, s = sqrt(5), r' = (3+sqrt(5))/2, s' = (5 + sqrt(5))/4.

Links

Table of n, a(n) for n=1..56.

Example

(1)  v o u = (2, 6, 8, 13, 17, 20, 24, 26, 31, 35, 38, 42, ...) = A356217
(2)  v' o u = (1, 5, 7, 10, 14, 16, 19, 21, 25, 28, 30, 34, ...) = A356218
(3)  v o u' = (4, 11, 15, 22, 29, 33, 40, 44, 51, 58, 62, 76, ...) = A190509
(4)  v' o u' = (3, 9, 12, 18, 23, 27, 32, 36, 41, 47, 50, 56, ...) = A356220

Mathematica

z = 1000;
u = Table[Floor[n*(1 + Sqrt[5])/2], {n, 1, z}];  (* A000201 *)
u1 = Complement[Range[Max[u]], u];  (* A001950 *)
v = Table[Floor[n*Sqrt[5]], {n, 1, z}];  (* A022839 *)
v1 = Complement[Range[Max[v]], v];  (* A108598 *)
zz = 120;
Table[v[[u[[n]]]], {n, 1, z/4}]   (* A356217 *)
Table[v1[[u[[n]]]], {n, 1, z/4}]  (* A356218 *)
Table[v[[u1[[n]]]], {n, 1, z/4}]  (* A190509 *)
Table[v1[[u1[[n]]]], {n, 1, z/4}] (* A356220 *)

Crossrefs

Cf. A000201, A001950, A022839, A108598, A351415 (intersections), A356104 (reverse composites), A356217, A356218, A356219.

Sequence in context: A310322 A261953 A297001 * A309394 A285564 A140979

Adjacent sequences: A356217 A356218 A356219 * A356221 A356222 A356223

Keyword

nonn,easy

Author

Clark Kimberling, Nov 13 2022

Status

approved