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a(n) = A137803(A001951(n)).
4

%I #12 Aug 24 2022 09:50:59

%S 1,3,7,9,13,15,17,21,22,26,28,30,34,36,40,42,45,47,49,53,55,59,61,63,

%T 66,68,72,74,78,80,82,86,88,91,93,95,99,101,105,107,109,112,114,118,

%U 120,124,126,128,132,133,137,139,141,145,147,151,153,156,158,160

%N a(n) = A137803(A001951(n)).

%C This is the first 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:

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

%C (2) v' o u;

%C (3) v o u';

%C (4) v' o u'.

%C 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 A356056 to A356059.

%C 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

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

%C For A356138, u, v, u', v', are the Beatty sequences given by u(n) = floor(n*sqrt(2)) and v(n) = floor(n*(1/2 + sqrt(2)), so that r = sqrt(2), s = 1/2 + sqrt(2), r' = 2 + sqrt(2), s' = (9 + 4*sqrt(2))/7.

%e (1) v o u = (1, 3, 7, 9, 13, 15, 17, 21, 22, 26, 28, 30, 34, ...) = A356138

%e (2) v' o u = (2, 4, 8, 10, 14, 16, 18, 23, 25, 29, 31, 33, 37, ...) = A356139

%e (3) v o u' = (5, 11, 19, 24, 32, 38, 44, 51, 57, 65, 70, 76, 84, ...) = A356140

%e (4) v' o u' = (6, 12, 20, 27, 35, 41, 48, 56, 62, 71, 77, 83, 92, ...) = A356141

%t z = 800;

%t u = Table[Floor[n (Sqrt[2])], {n, 1, z}]; (*A001951*)

%t u1 = Complement[Range[Max[u]], u] ; (*A001952*)

%t v = Table[Floor[n (1/2 + Sqrt[2])], {n, 1, z}]; (*A137803*)

%t v1 = Complement[Range[Max[v]], v] ; (*A137804*)

%t Table[v[[u[[n]]]], {n, 1, z/8}] (*A356138 *)

%t Table[v1[[u[[n]]]], {n, 1, z/8}] (* A356139*)

%t Table[v[[u1[[n]]]], {n, 1, z/8}] (* A356140 *)

%t Table[v1[[u1[[n]]]], {n, 1, z/8}] (* A356141 *)

%Y Cf. A001951, A001952, A137804.

%Y Cf. A356056, A356057, A356058, A356059, A356139, A356140, A356141.

%K nonn,easy

%O 1,2

%A _Clark Kimberling_, Aug 06 2022