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 A089607 #6 Mar 30 2012 18:39:21 %S A089607 1,3,1,3,3,1,1,3,3,3,1,1,3,1,1,3,3,3,1,3,3,1,1,1,3,3,1,1,3,1,1,3,3,3, %T A089607 1,3,3,1,1,3,3,3,1,1,3,1,1,1,3,3,1,3,3,1,1,1,3,3,1,1,3,1,1,3,3,3,1,3, %U A089607 3,1,1,3,3,3,1,1,3,1,1,3,3,3,1,3,3,1,1,1,3,3,1,1,3,1,1,1,3,3,1,3,3,1,1,3,3 %N A089607 a(n)=((-1)^(n+1)*A002425(n)) modulo 4. %F A089607 a(1)=1; for n>=2, a(n) = 2*A014577(n-1)+1 %o A089607 (PARI) a(n)=numerator(2/n*(4^n-1)*bernfrac(2*n))%4 %Y A089607 Cf. A056832. %K A089607 nonn %O A089607 1,2 %A A089607 _Benoit Cloitre_, Dec 30 2003