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 A064671 #15 Dec 16 2017 12:55:30 %S A064671 0,3,18,91,420,1829,7686,31623,128520,518665,2084874,8361995,33497100, %T A064671 134094861,536608782,2146926607,8588754960,34357248017,137433710610, %U A064671 549744803859,2199000186900,8796044787733,35184271425558,140737278640151,562949517213720 %N A064671 Number of n-digit base 4 biquanimous numbers (with leading 0's allowed, but not all-0 string). %C A064671 A number is biquanimous (A064544) if its digits can be split into two groups with the same sum. - _David W. Wilson_, SeqFan memo, Oct 08 2001. %F A064671 Empirical g.f.: x^2*(3 - 12*x + 22*x^2 - 16*x^3) / ((1 - x)^2*(1 - 2*x)^2*(1 - 4*x)). [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009] %F A064671 Conjectures from _Colin Barker_, Dec 16 2017: (Start) %F A064671 a(n) = (2^n-2) * (1+2^n-n) / 2. %F A064671 a(n) = 10*a(n-1) - 37*a(n-2) + 64*a(n-3) - 52*a(n-4) + 16*a(n-5) for n>5. %F A064671 (End) %K A064671 nonn,base %O A064671 1,2 %A A064671 _John W. Layman_, Oct 09 2001 %E A064671 More terms from _Christian G. Bower_, Oct 12 2001