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A225875 We write the 1 + 4*k numbers once and twice the others. 0

%I

%S 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,

%T 17,18,18,19,19,20,20,21,22,22,23,23,24,24,25,26,26,27,27,28,28,29,30,

%U 30,31,31,32,32,33,34,34,35,35,36,36,37,38,38,39,39,40,40,41,42,42,43

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

%C First differences are periodic with period 7.

%H <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 0, 0, 0, 1, -1).

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

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

%F a(n) = n - floor(3*n/7). - _Wesley Ivan Hurt_, Sep 29 2017

%t t = {}; Do[If[Mod[n, 4] == 1, AppendTo[t, n], AppendTo[t, {n, n}]], {n, 50}]; Flatten[t] (* _T. D. Noe_, May 23 2013 *)

%t LinearRecurrence[{1, 0, 0, 0, 0, 0, 1, -1},{1, 2, 2, 3, 3, 4, 4, 5},74] (* _Ray Chandler_, Aug 26 2015 *)

%t 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 *)

%Y Cf. A132270.

%K nonn,easy

%O 1,2

%A _José María Grau Ribas_, May 19 2013

%E Corrected, extended, and edited by _Ralf Stephan_, May 20 2013

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Last modified November 14 17:24 EST 2019. Contains 329126 sequences. (Running on oeis4.)