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%I #16 Oct 22 2019 10:17:21
%S 4,9,21,49,115,270,634,1489,3498,8218,19307,45359,106565,250361,
%T 588192,1381884,3246565,7627402,17919636,42099965,98908653,232373629,
%U 545933059,1282602102,3013314774,7079409829,16632196530,39075285666,91802543767,215678705823
%N Pisot sequence L(4,9).
%H Colin Barker, <a href="/A048582/b048582.txt">Table of n, a(n) for n = 0..1000</a>
%F a(n) = 3*a(n-1) - 2*a(n-2) + a(n-3) + a(n-4) - 2*a(n-5) + a(n-6) - a(n-7) (conjectured). Recurrence is satisfied for at least 760000 terms. - _Chai Wah Wu_, Jul 25 2016
%F Note the warning in A010925 from Pab Ter (pabrlos(AT)yahoo.com), May 23 2004: [A010925] and other examples show that it is essential to reject conjectured generating functions for Pisot sequences until a proof or reference is provided. - _N. J. A. Sloane_, Jul 26 2016
%t a[n_] := a[n] = Switch[n, 0, 4, 1, 9, _, Ceiling[a[n-1]^2/a[n-2]]];
%t a /@ Range[0, 29] (* _Jean-François Alcover_, Oct 22 2019 *)
%o (PARI) pisotL(nmax, a1, a2) = {
%o a=vector(nmax); a[1]=a1; a[2]=a2;
%o for(n=3, nmax, a[n] = ceil(a[n-1]^2/a[n-2]));
%o a
%o }
%o pisotL(50, 4, 9) \\ _Colin Barker_, Aug 07 2016
%Y See A008776 for definitions of Pisot sequences.
%K nonn
%O 0,1
%A _David W. Wilson_
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