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A101883 Write four numbers, skip one, write four, skip two, write four, skip three... and so on.

%I A101883 #14 Aug 11 2016 05:48:12
%S A101883 1,2,3,4,6,7,8,9,12,13,14,15,19,20,21,22,27,28,29,30,36,37,38,39,46,
%T A101883 47,48,49,57,58,59,60,69,70,71,72,82,83,84,85,96,97,98,99,111,112,113,
%U A101883 114,127,128,129,130,144,145,146,147,162,163,164,165,181,182,183,184,201
%N A101883 Write four numbers, skip one, write four, skip two, write four, skip three... and so on.
%C A101883 Union of A051936, A051936+1, A051936+2, and A051936+3. - _Ivan Neretin_, Aug 03 2016
%C A101883 First terms of the four repeated terms belong to A051936. - _Michael De Vlieger_, Aug 03 2016
%H A101883 Ivan Neretin, <a href="/A101883/b101883.txt">Table of n, a(n) for n = 1..10000</a>
%H A101883 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,2,-2,0,0,-1,1).
%F A101883 G.f.: x*(1+x+x^2+x^3-x^5-x^6-x^7)/ ((1+x)^2 * (x^2+1)^2 * (1-x)^3). [Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009; checked and corrected by _R. J. Mathar_, Sep 16 2009]
%t A101883 LinearRecurrence[{1,0,0,2,-2,0,0,-1,1},{1,2,3,4,6,7,8,9,12},80] (* or *) Rest[CoefficientList[Series[x*(1+x+x^2+x^3-x^5-x^6-x^7)/((1+x)^2(x^2+1)^2(1-x)^3),{x,0,80}],x]](* _Harvey P. Dale_, Jan 19 2016 *)
%t A101883 Table[Range[#, # + 3] &[n (n + 1)/2 - 9], {n, 4, 20}] // Flatten (* _Michael De Vlieger_, Aug 03 2016 *)
%Y A101883 Cf. A000217, A051936, A101881, A101882.
%K A101883 easy,nonn
%O A101883 1,2
%A A101883 Candace Mills (scorpiocand(AT)yahoo.com), Dec 19 2004