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 A153207 #9 Sep 08 2022 08:45:39
%S A153207 3,5,13,61,157,277,421,661,733,877,997,1093,1213,1237,1381,1933,2797,
%T A153207 3253,3517,3733,4021,4261,4621,5413,6037,6133,6637,6781,6997,7213,
%U A153207 7477,7933,8053,8221,9013,9133,9277,9661,10357,10453,10861,10957,11317,11677
%N A153207 Primes of the form 2*p-1 where p is prime and p-1 is squarefree.
%C A153207 Subsequence of A005383.
%e A153207 For p = 2 (the only case with p-1 odd), 2*p-1 = 3 is prime and p-1 = 1 is squarefree, so 3 is in the sequence. For p = 19, 2*p-1 = 37 is prime and p-1 = 18 is not squarefree, so 37 is not in the sequence.
%t A153207 lst={}; Do[p = Prime[n]; If[SquareFreeQ[Floor[p/2]] && PrimeQ[Ceiling[p/2]], AppendTo[lst, p]], {n, 7!}]; lst
%o A153207 (Magma) [ q: p in PrimesUpTo(5900) | IsSquarefree(p-1) and IsPrime(q) where q is 2*p-1 ];
%Y A153207 Cf. A005117 (squarefree numbers), A005383 (numbers n such that both n and (n+1)/2 are primes), A153208, A153209, A153210.
%K A153207 nonn
%O A153207 1,1
%A A153207 _Vladimir Joseph Stephan Orlovsky_, Dec 20 2008
%E A153207 Edited by _Klaus Brockhaus_, Dec 24 2008
%E A153207 Mathematica updated by _Jean-François Alcover_, Jul 04 2013