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 A171733 #8 Jun 13 2015 00:53:27 %S A171733 -1,1,1,7,31,41,137,151,391,409,889,911,1751,1777,3121,3151,5167,5201, %T A171733 8081,8119,12079,12121,17401,17447,24311,24361,33097,33151,44071, %U A171733 44129,57569,57631,73951,74017,93601,93671,116927,117001,144361,144439,176359,176441,213401,213487,255991 %N A171733 a(2n)=A165568(n). a(2n+1)=A165563(n). %H A171733 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (1,4,-4,-6,6,4,-4,-1,1). %F A171733 a(n) = n^3/8 +n^2/16 -15/32 +n^4/16 +(-1)^n*( n^3/8+3*n^2/16-n-17/32 ). %F A171733 G.f.: ( 1-2*x-4*x^2+2*x^3-18*x^4+2*x^5-4*x^6-2*x^7+x^8 ) / ( (1+x)^4*(-1+x)^5 ). %F A171733 a(n)= +a(n-1) +4*a(n-2) -4*a(n-3) -6*a(n-4) +6*a(n-5) +4*a(n-6) -4*a(n-7) -a(n-8) +a(n-9). %o A171733 (PARI) A171733(n)=if( bittest(n,0), n, -1-n) +(n\=2)^2 +2*n^3 +n^4 %Y A171733 Cf. A035287. %K A171733 sign,easy %O A171733 0,4 %A A171733 _Paul Curtz_, Dec 17 2009