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 A106221 #7 Mar 14 2015 09:57:56
%S A106221 1,1,-1,2,-4,10,-26,71,-199,569,-1652,4855,-14413,43153,-130143,
%T A106221 394967,-1205268,3695771,-11381215,35183209,-109138163,339599993,
%U A106221 -1059702401,3315256789,-10396158911,32671424776,-102879610571,324557399534,-1025643986057,3246330348415,-10290418283163
%N A106221 Self-convolution 4th power equals A106220, which consists entirely of digits {0,1,2,3} after the initial terms {1,4}.
%F A106221 Limit a(n+1)/a(n) = -3.30697774878897620974321728382452592372871...
%e A106221 A(x) = 1 + x - x^2 + 2*x^3 - 4*x^4 + 10*x^5 - 26*x^6 + 71*x^7 -+...
%e A106221 A(x)^4 = 1 + 4*x + 2*x^2 + 3*x^4 + 2*x^6 + x^8 + 2*x^14 +...
%e A106221 A106220 = {1,4,2,0,3,0,2,0,1,0,0,0,0,0,2,0,0,0,2,...}.
%o A106221 (PARI) {a(n)=local(A=1+4*x);if(n==0,1, for(j=1,n, for(k=0,3,t=polcoeff((A+k*x^j+x*O(x^j))^(1/4),j); if(denominator(t)==1,A=A+k*x^j;break))); return(polcoeff((A+x*O(x^n))^(1/4),n)))}
%Y A106221 Cf. A106220, A106219, A106223, A106225.
%K A106221 sign,base
%O A106221 0,4
%A A106221 _Paul D. Hanna_, May 01 2005