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 A243967 #10 Jan 19 2015 14:48:01 %S A243967 1,3,5,0,5,0,6,1,2,5,1,3,1,1,7,1,5,3,0,3,3,1,8,3,7,6,7,7,2,2,6,2,4,1, %T A243967 5,9,7,2,5,2,3,0,6,9,8,0,3,1,3,0,1,9,2,5,5,8,6,0,9,7,8,4,0,6,1,6,4,5, %U A243967 0,7,4,0,0,8,8,8,8,1,5,1,3,5,8,8,9,8,3,4,8,3,5,5,6,8,5,1,5,1,1 %N A243967 Decimal expansion of 'xi', a constant related to the second order quadratic recurrence q(0)=q(1)=1, q(n)=q(n-2)*(q(n-1)+1). %D A243967 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 6.10 Quadratic recurrence constants, pp. 445-446. %F A243967 q(n) = floor(xi^(phi^n)*eta^((1-phi)^n)) where phi is the golden ratio (1+sqrt(5))/2 and eta is A243968. %e A243967 1.3505061251311715303318376772262415972523... %t A243967 digits = 99; n0 = 5; dn = 5; Clear[q]; q[0] = q[1] = 1; q[n_] := q[n] = q[n - 2] (q[n - 1] + 1); xi[n_] := xi[n] = ((q[n] - 1)^(1/2*( Sqrt[5] - 1))*(q[n + 1] - 1))^((1/2*( Sqrt[5] - 1))^n/Sqrt[5]); xi[n0]; xi[n = n0 + dn]; While[RealDigits[xi[n], 10, digits + 10] != RealDigits[xi[n - 5], 10, digits + 10], Print["n = ", n]; n = n + dn]; RealDigits[xi[n], 10, digits] // First %Y A243967 Cf. A006277, A243968 (eta). %K A243967 nonn,cons %O A243967 1,2 %A A243967 _Jean-François Alcover_, Jun 16 2014