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 A321002 #20 Nov 19 2018 09:15:11 %S A321002 3,19,118,716,4312,25904,155488,933056,5598592,33592064,201553408, %T A321002 1209322496,7255939072,43535642624,261213872128,1567283265536, %U A321002 9403699658752,56422198083584,338533188763648,2031199133106176,12187194799685632,73123168800210944,438739012805459968,2632434076841148416 %N A321002 a(0)=3; thereafter a(n) = 20*6^(n-1)-2^(n-1). %C A321002 Conjectured to be the sum of A175046(i) for 2^n <= i < 2^(n+1). %C A321002 Conjecture is true (see comments in A175046). - _Chai Wah Wu_, Nov 18 2018 %H A321002 Colin Barker, <a href="/A321002/b321002.txt">Table of n, a(n) for n = 0..1000</a> %H A321002 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-12). %F A321002 From _Colin Barker_, Nov 02 2018: (Start) %F A321002 G.f.: (1 - x)*(3 - 2*x) / ((1 - 2*x)*(1 - 6*x)). %F A321002 a(n) = 8*a(n-1) - 12*a(n-2) for n>2. %F A321002 (End) %o A321002 (PARI) Vec((1 - x)*(3 - 2*x) / ((1 - 2*x)*(1 - 6*x)) + O(x^25)) \\ _Colin Barker_, Nov 02 2018 %o A321002 (PARI) a(n) = if (n, 20*6^(n-1)-2^(n-1), 3); \\ _Michel Marcus_, Nov 02 2018 %Y A321002 Essentially the first differences of A321003. %Y A321002 Cf. A175046. %K A321002 nonn,easy %O A321002 0,1 %A A321002 _N. J. A. Sloane_, Nov 01 2018