A225875 We write the 1 + 4*k numbers once and twice the others.

1, 2, 2, 3, 3, 4, 4, 5, 6, 6, 7, 7, 8, 8, 9, 10, 10, 11, 11, 12, 12, 13, 14, 14, 15, 15, 16, 16, 17, 18, 18, 19, 19, 20, 20, 21, 22, 22, 23, 23, 24, 24, 25, 26, 26, 27, 27, 28, 28, 29, 30, 30, 31, 31, 32, 32, 33, 34, 34, 35, 35, 36, 36, 37, 38, 38, 39, 39, 40, 40, 41, 42, 42, 43

Offset

1,2

Comments

First differences are periodic with period 7.

Links

Table of n, a(n) for n=1..74.

Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 0, 0, 1, -1).

Formula

a(n+1) = 1 + 4*floor(n/7) + [0,1,1,2,2,3,3].

G.f.: x*(1 + x + x^3 + x^5)/((1-x)^2 * (1 + x + x^2 + x^3 + x^4 + x^5 + x^6)).

a(n) = n - floor(3*n/7). - Wesley Ivan Hurt, Sep 29 2017

Mathematica

t = {}; Do[If[Mod[n, 4] == 1, AppendTo[t, n], AppendTo[t, {n, n}]], {n, 50}]; Flatten[t] (* T. D. Noe, May 23 2013 *)
LinearRecurrence[{1, 0, 0, 0, 0, 0, 1, -1}, {1, 2, 2, 3, 3, 4, 4, 5}, 74] (* Ray Chandler, Aug 26 2015 *)
Table[If[Mod[n, 4] == 1, n, {n, n}], {n, 50}] // Flatten (* or *) Drop[ Flatten[ Table[{n, n}, {n, 50}]], {1, -1, 8}] (* Harvey P. Dale, Feb 03 2019 *)

Crossrefs

Cf. A132270.

Sequence in context: A100679 A226190 A195182 * A189688 A092982 A302930

Adjacent sequences: A225872 A225873 A225874 * A225876 A225877 A225878

Keyword

nonn,easy

Author

José María Grau Ribas, May 19 2013

Extensions

Corrected, extended, and edited by Ralf Stephan, May 20 2013

Status

approved