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 A167402 #2 May 10 2013 12:45:52 %S A167402 0,0,4,12,44,116,356,948,2772,7396,20972,56108,156236,418228,1151556, %T A167402 3081180,8421052,22514652,61207972,163518308,442769316,1181982628, %U A167402 3190663628,8511628124,22920057932,61104234356,164212633412 %N A167402 Number of n-step walks on square lattice, self-avoiding until the last step. %C A167402 A001411(n)=4^n-(a(n)+4*(a(n-1)+4*(a(n-2)+...))) %F A167402 a(n) = 4*A001411(n-1)-A001411(n), n>0. [From _Vladeta Jovovic_, Nov 02 2009] %Y A167402 See references given for A001411. %K A167402 nonn %O A167402 0,3 %A A167402 Vadim Sheikhman (vvsshh(AT)gmail.com), Nov 02 2009 %E A167402 More terms from _Vladeta Jovovic_, Nov 02 2009