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 A117545 #5 Apr 15 2014 02:34:19
%S A117545 2,2,1,1,3,1,5,1,6,2,9,1,5,1,3,2,3,1,19,1,3,2,5,1,6,4,3,2,5,1,7,1,3,6,
%T A117545 21,2,10,1,6,2,3,1,5,1,19,2,10,1,14,3,6,2,11,1,6,4,3,2,3,1,7,1,5,204,
%U A117545 12,2,6,1,3,2,3,1,5,1,3,6,3,2,5,1,6,2,5,1,5,11,7,2,3,1,6,12,7,4,7,2,17,1,3
%N A117545 Least k such that Phi(k,n), the k-th cyclotomic polynomial evaluated at n, is prime.
%C A117545 Note that a(n)=1 iff n-1 is prime because Phi(1,x)=x-1. For n<2048, we have the bound a(n)<251. However, a(2048) is greater than 10000. Is a(n) defined for all n? For fixed n, there are many sequences listing the k that make Phi(k,n) prime: A000043, A028491, A004061, A004062, A004063, A004023, A005808, A016054, A006032, A006033, A006034, A006035.
%H A117545 T. D. Noe, <a href="/A117545/b117545.txt">Table of n, a(n) for n = 1..2047</a>
%t A117545 Table[k=1; While[ !PrimeQ[Cyclotomic[k,n]], k++ ]; k, {n,100}]
%Y A117545 Cf. A117544 (least k such that Phi(n, k) is prime).
%K A117545 nonn
%O A117545 1,1
%A A117545 _T. D. Noe_, Mar 28 2006