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 A334991 #25 Jun 04 2020 12:19:16 %S A334991 4,58,988,17560,315184,5669728,102040768,1836676480,33059947264, %T A334991 595078133248,10711402728448,192805234432000,3470494161055744, %U A334991 62468894664122368,1124440103014678528,20239921850506117120,364318593294077722624,6557734679233269465088,118039224225958332203008 %N A334991 a(n) = 4^n + 3 * 18^n. %C A334991 This sequence is a variation of the sequence A333385, variation proposed by Tony Gardiner in his book in reference. %C A334991 Proposition: a(n) is a perfect square iff n = 0; in this case, a(0) = 4. %D A334991 A. Gardiner, The Mathematical Olympiad Handbook: An Introduction to Problem Solving, Oxford University Press, 1997, reprinted 2011, page 115 (1991). %H A334991 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (22,-72). %F A334991 a(n) = A000302(n) + 3 * A001027(n). %F A334991 a(n) = 22*a(n-1) - 72*a(n-2) for n>1. %F A334991 G.f.: (4 - 30*x)/((1 - 4*x)*(1 - 18*x)). - _Alejandro J. Becerra Jr._, Jun 01 2020 %e A334991 a(4) = 4^4 + 3 * 18^4 = 315184 = 2^4 * 19699 is not a perfect square. %p A334991 S:=seq(4^n+3*18^n, n=0..20); %Y A334991 Cf. A000302, A001027, A333385. %K A334991 nonn,easy %O A334991 0,1 %A A334991 _Bernard Schott_, May 18 2020