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 A280170 #17 Sep 08 2022 08:46:18
%S A280170 19,41,79,101,109,137,139,199,271,281,311,379,401,439,461,499,521,601,
%T A280170 619,641,701,727,739,761,769,811,821,859,881,919,941,953,1013,1039,
%U A280170 1061,1087,1181,1279,1301,1361,1399,1429,1459,1481,1549,1579,1601,1699,1721,1759,1777,1871,1879,1901
%N A280170 Primes p such that both 2^(p-1) - 1 and 2^(p+1) - 1 are not squarefree.
%e A280170 19 is in this sequence because 2^(19-1) - 1 = 262143 = 3^3*7*19*73 and 2^(19+1) - 1 = 1048575 = 3*5^2*11*31*41.
%t A280170 Select[Prime[Range[200]], ! SquareFreeQ[ 2^(#-1) - 1 ] && ! SquareFreeQ[ 2^(#+1) - 1 ] &] (* _Robert Price_, Feb 26 2017 *)
%t A280170 Select[Prime[Range[300]],NoneTrue[{2^(#-1)-1,2^(#+1)-1},SquareFreeQ]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 14 2020 *)
%o A280170 (Magma) [p: p in PrimesUpTo(200) | not IsSquarefree(2^(p-1)-1) and not
%o A280170 IsSquarefree(2^(p+1)-1)];
%o A280170 (PARI) is(n)=isprime(n) && !issquarefree(2^(n-1)-1) && !issquarefree(2^(n+1)-1) \\ _Charles R Greathouse IV_, Aug 26 2017
%Y A280170 Cf. A013929, A049094, A280149.
%K A280170 nonn
%O A280170 1,1
%A A280170 _Juri-Stepan Gerasimov_, Dec 27 2016
%E A280170 Inserted terms 727 and 739 by _Robert Price_, Feb 26 2017
%E A280170 Added terms a(38)-a(54) by _Robert Price_, Feb 26 2017