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 A093812 #3 Mar 31 2012 13:20:56 %S A093812 1,15,17,1680,421,56086995,9940915081637, %T A093812 31271643639794562523698024915, %U A093812 3090319883395626207270178075850946683940891639487741952,9721376888636052447184767296534734059409700304429485542107645657085305 %N A093812 a(1) = 1; for n > 1, a(n) is the smallest positive integer not already used such that a(n)*a(n-1) + 1 is a fourth power. %C A093812 The next terms are (to two significant digits) 9.6*10^95, 3.0*10^111, 3.0*10^137, 9.4*10^152, 9.3*10^178. %e A093812 The 4th roots of unity mod 17 are 1, 4, 13 and 16. (4^4 - 1)/17 = 15, which has already been used, so 17 is followed by (13^4 - 1)/17 = 1680. %Y A093812 Cf. A091569, A083203. %K A093812 nonn %O A093812 1,2 %A A093812 _David Wasserman_, May 20 2004