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 A171408 #8 Aug 15 2015 16:07:53 %S A171408 4,4,4,4,0,-12,-32,-52,-52,0,136,356,576,576,0,-1508,-3948,-6388, %T A171408 -6388,0,16724,43784,70844,70844,0,-185472,-485572,-785672,-785672,0, %U A171408 2056916,5385076,8713236,8713236,0,-22811548,-59721408,-96631268,-96631268,0,252983944,662320564 %N A171408 a(n) = A171373(n+1) - 2*A171373(n). %C A171408 The least significant digits have a period of length 20. Another period (not the same but of the same length, as this a sequence contains negative numbers) is defined reading the sequence modulo 10. %H A171408 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-4,2,-1) %F A171408 a(n)=4*A105371(n-1), n>0. %F A171408 a(n)= 3*a(n-1) -4*a(n-2) +2*a(n-3) -a(n-4). G.f.: 4*(1-2*x+2*x^2)/(1-3*x+4*x^2-2*x^3+x^4). %Y A171408 Cf. A138112, A105371. %K A171408 sign %O A171408 0,1 %A A171408 _Paul Curtz_, Dec 08 2009 %E A171408 Edited and extended by _R. J. Mathar_, Mar 02 2010