This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072257 #18 Sep 08 2022 08:45:06
%S A072257 -6,-15,-27,21,597,4437,25941,136533,677205,3233109,15029589,68506965,
%T A072257 307582293,1364546901,5995058517,26127717717,113100805461,
%U A072257 486762960213,2084490794325,8887718991189
%N A072257 a(n) = ((6*n-17)*4^n - 1)/3.
%C A072257 Related to Collatz function (for n>2). All terms are divisible by 3.
%H A072257 Harvey P. Dale, <a href="/A072257/b072257.txt">Table of n, a(n) for n = 0..1000</a>
%H A072257 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (9,-24,16).
%F A072257 G.f.: -3*(2-13*x+12*x^2)/((1-x)*(1-4*x)^2). - _Bruno Berselli_, Dec 16 2011
%F A072257 E.g.f.: (-1/3)*( (17-24*x)*exp(4*x) + exp(x) ). - _G. C. Greubel_, Jan 14 2020
%p A072257 seq( ((6*n-17)*4^n -1)/3, n=0..40); # _G. C. Greubel_, Jan 14 2020
%t A072257 LinearRecurrence[{9,-24,16},{-6,-15,-27},40] (* _Harvey P. Dale_, Nov 23 2015 *)
%o A072257 (PARI) a(n)=((6*n-17)*4^n-1)/3 \\ _Charles R Greathouse IV_, Oct 07 2015
%o A072257 (Magma) [((6*n-17)*4^n -1)/3: n in [0..40]]; // _G. C. Greubel_, Jan 14 2020
%o A072257 (Sage) [((6*n-17)*4^n -1)/3 for n in (0..40)] # _G. C. Greubel_, Jan 14 2020
%o A072257 (GAP) List([0..40], n-> ((6*n-17)*4^n -1)/3); # _G. C. Greubel_, Jan 14 2020
%Y A072257 Cf. A072258, A072259, A072260.
%K A072257 sign,easy
%O A072257 0,1
%A A072257 N. Rathankar (rathankar(AT)yahoo.com), Jul 08 2002
%E A072257 Edited and extended by _Henry Bottomley_, Aug 06 2002