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 A261539 #46 Sep 08 2022 08:46:13 %S A261539 0,1,2,3,6,9,12,21,42,150,195,390,411,1215,2754,2757,3246,6186,11340, %T A261539 12885,84708,87120,191772,503919,786441 %N A261539 Numbers m such that (4^m + 5) / 3 is prime. %C A261539 After 1, m is not of the form 3*k+1 because in this case 4^m+5 is divisible by 9; after 2, m is not of the form 3*k+2 because in this case 4^m+5 is divisible by 7. Therefore, m>2 is always a multiple of 3. - _Bruno Berselli_, Aug 25 2015 %C A261539 Larger members of the sequence generate probable primes only. - _Serge Batalov_, Aug 27 2015 %H A261539 Henri & Renaud Lifchitz PRPtop, <a href="http://www.primenumbers.net/prptop/searchform.php?form=%282%5En%2B5%29%2F3&action=Search">(2^n+5)/3 PRPs</a> %e A261539 6 is in the sequence because (4^6+5)/3 = 1367 is prime. %e A261539 9 is in the sequence because (4^9+5)/3 = 87383 is prime. %e A261539 4 is not in the sequence because (4^4+5)/3 = 87 = 3*29 is not prime. %t A261539 Select[Range[0, 5000], PrimeQ[(4^# + 5)/3] &] %o A261539 (Magma) [n: n in [0..1000] | IsPrime((4^n+5) div 3)]; %o A261539 (PARI) isok(n)=isprime((4^n + 5) / 3) \\ _Anders Hellström_, Aug 25 2015 %Y A261539 Cf. A163834. %Y A261539 Cf. numbers n such that (4^n+k)/3 is prime: this sequence (k=5), A261577 (k=11), A261578 (k=17), A261579 (k=23). %Y A261539 Cf. A253772. %K A261539 nonn,more %O A261539 1,3 %A A261539 _Vincenzo Librandi_, Aug 25 2015 %E A261539 a(18)-a(23) from Lelio R Paula (2012-2014) via _Serge Batalov_, Aug 27 2015 %E A261539 a(24)-a(25) from _Serge Batalov_, Aug 29 2015