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 A125871 #11 Aug 02 2025 13:17:14
%S A125871 2,3,5,8,9,14,15,20,24,27,30,32,35,45,48,50,54,63,72,75,98,105,144,
%T A125871 162,180,189,192,200,224,240,252,300,320,420,450,500,504,525,540,560,
%U A125871 588,630,750,768,864,875,900,960,980,1029,1080,1134,1215,1280,1323
%N A125871 Numbers k such that p=14*k+1 is prime and cos(2*Pi/p) is an algebraic number of a 7-smooth degree, but not 5-smooth.
%C A125871 Numbers k such that p=14*k+1 is prime and the greatest prime divisor of p-1 is 7.
%t A125871 Do[If[Take[FactorInteger[EulerPhi[14n+1]][[ -1]],1]=={7} && PrimeQ[14n+1],Print[n]],{n,1,10000}]
%Y A125871 Cf. A125866-A125878.
%K A125871 nonn
%O A125871 1,1
%A A125871 _Artur Jasinski_, Dec 13 2006
%E A125871 Edited by _Don Reble_, Apr 24 2007