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 A125869 #10 Aug 02 2025 14:30:13
%S A125869 1,3,4,6,10,15,18,24,25,27,40,54,60,64,75,81,120,160,162,180,216,225,
%T A125869 300,400,405,480,486,648,768,810,864,900,960,972,1125,1440,1536,1600,
%U A125869 1944,2160,2187,2250,2304,2400,2560,3240,3375,3645,3750,4096,4320
%N A125869 Numbers k such that p=10*k+1 is prime and cos(2*Pi/p) is an algebraic number of a 5-smooth degree, but not 3-smooth.
%C A125869 Numbers k such that p=10*k+1 is prime and the greatest prime divisor of p-1 is 5.
%t A125869 Do[If[Take[FactorInteger[EulerPhi[10n+1]][[ -1]],1]=={5} && PrimeQ[10n+1],Print[n]],{n,1,10000}]
%Y A125869 Cf. A024912, A125866-A125878.
%K A125869 nonn
%O A125869 1,2
%A A125869 _Artur Jasinski_, Dec 13 2006
%E A125869 Edited by _Don Reble_, Apr 24 2007