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 A125878 #29 Jan 23 2022 12:45:03 %S A125878 3,7,11,29,23,53,103,191,47,59,311,149,83,173,283,107,709,367,269,569, %T A125878 293,317,167,179,389,607,619,643,1091,227,509,263,823,557,1193,907, %U A125878 1571,653,2339,347,359,1087,383,773,3547,797,2111,2677,5449,2749,467 %N A125878 Duplicate of A066674. %C A125878 Original name was: a(n) = the least number k such that cos(2pi/k) is an algebraic number of a prime(n)-smooth degree, but not prime(n-1)-smooth. %C A125878 Comments from _N. J. A. Sloane_, Jan 07 2013: (Start) %C A125878 This is a duplicate of A066674. This follows from the following argument. The degree of the minimal polynomial of cos(2*Pi/k) is phi(k)/2, where phi is Euler's totient function. Then a(n) is the least number k such that prime(n) is the largest prime dividing phi(k) and prime(n-1) does not divide phi(k)/2. For the rest of the proof see Bjorn Poonen's remarks in A066674. %C A125878 It also seems likely that this is the same as A035095, but this is an open problem. %C A125878 Conjecture: this sequence contains only primes (this would follow if this is indeed the same as A035095). %C A125878 (End) %D A125878 See A181877. %Y A125878 Cf. A066674, A035095, A125866-A125877. %K A125878 dead %O A125878 1,1 %A A125878 _Artur Jasinski_, Dec 13 2006 %E A125878 Edited by _Don Reble_, Apr 24 2007 %E A125878 Minor edits by _Ray Chandler_, Oct 20 2011