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 A268061 #25 Jan 20 2024 18:57:09 %S A268061 3,7,15,59,6127,8703,11619,23403,124299 %N A268061 Numbers k such that 7*8^k - 1 is prime. %C A268061 a(10) > 2*10^5. %C A268061 Terms are A001771(n)/3 that are integers. %D A268061 R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3. %H A268061 H. C. Williams, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa39/aa3912.pdf">The primality of certain integers of the form 2Ar^n - 1</a>, Acta Arith. 39 (1981), 7-17. %t A268061 Select[Range[0, 200000], PrimeQ[7*8^# - 1] &] %o A268061 (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*8^n-1), print1(n, ", "))) \\ _Altug Alkan_, Jan 25 2016 %Y A268061 Cf. similar sequences of the form k*(k+1)^n-1: A003307 (k=2), ... (k=3), A046865 (k=4), A079906 (k=5), A046866 (k=6), this sequence (k=7), ... (k=8), A056725 (k=9), A046867 (k=10), A079907 (k=11). %Y A268061 Cf. A001771, A002235, A005541, A247260. %K A268061 nonn,hard,more %O A268061 1,1 %A A268061 _Robert Price_, Jan 25 2016