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%I #19 Jul 03 2018 02:27:04
%S 2,2,8,20,60,170,492,1414,4074,11728,33772,97240,279994,806208,
%T 2321386,6684162,19246280,55417452,159568196,459458306,1322957468,
%U 3809304206,10968454314,31582405472,90937912212,261845282320,753953441490
%N 4-wave sequence beginning with 2's with middles dropped.
%H Harry J. Smith, <a href="/A060823/b060823.txt">Table of n, a(n) for n = 2..200</a>
%H F. v. Lamoen, <a href="http://home.wxs.nl/~lamoen/wiskunde/wave.htm">Wave sequences</a>
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,-1,-1).
%F a(n) = 2*a(n-1) + 3*a(n-2) - a(n-3) - a(n-4). - Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 22 2003
%F From _R. J. Mathar_, Jul 15 2009: (Start)
%F G.f.: -2*x^2*(-1+x+x^2)/((1+x)*(x^3-3*x+1)).
%F a(n) = 2*A006357(n-3). (End)
%t LinearRecurrence[{2,3,-1,-1},{2,2,8,20},30] (* _Harvey P. Dale_, Aug 31 2016 *)
%o (PARI) { for (n=2, 200, if (n>5, a=2*a1 + 3*a2 - a3 - a4; a4=a3; a3=a2; a2=a1; a1=a, if (n==2, a=a4=2, if (n==3, a=a3=2, if (n==4, a=a2=8, a=a1=20)))); write("b060823.txt", n, " ", a); ) } \\ _Harry J. Smith_, Jul 12 2009
%Y Cf. A038197.
%K easy,nonn
%O 2,1
%A _Jason Earls_, May 01 2001
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