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 A379020 #46 Jun 18 2025 01:03:36
%S A379020 5,7,9,13,33,37,57,63,93,127,129,165,189,369,717,3079,3087,3925,6709,
%T A379020 7633,18001,21961,55557,60415,63589,69463,75949,98265,212295,416773,
%U A379020 647545,824325,1538959,2020893,2421175
%N A379020 Numbers k such that 2^k - 25 is prime.
%C A379020 Except for a(1), all terms are congruent to 1 or 3 mod 6.
%C A379020 a(36) > 3400000. - _Boyan Hu_, Jun 16 2025
%H A379020 Henri Lifchitz and Renaud Lifchitz (Editors), <a href="http://www.primenumbers.net/prptop/searchform.php?form=2%5En-25">Search for 2^n-25</a>, PRP Top Records.
%H A379020 Boyan Hu, <a href="https://sites.google.com/ocdsb.ca/2n25">2^n-25 PRP searching progress</a>
%e A379020 7 is in the sequence because 2^7-25=103 is prime.
%e A379020 8 is not in the sequence because 2^8-25=231=3*7*11 is not prime.
%t A379020 Do[ If[ PrimeQ[ 2^n - 25 ], Print[ n ] ], { n, 1, 15000} ]
%o A379020 (PARI) is(n)=ispseudoprime(2^n-25)
%Y A379020 Sequences of numbers k such that 2^k - d is prime: A000043 (d=1), A050414 (d=3), A059608 (d=5), A059609 (d=7), A059610 (d=9), A096817 (d=11), A096818 (d=13), A059612 (d=15), A059611 (d=17), A096819 (d=19), A096820 (d=21), A057220 (d=23), A356826 (d=29).
%Y A379020 Except for a(1), subsequence of A047241.
%K A379020 nonn,more
%O A379020 1,1
%A A379020 _Boyan Hu_, Dec 13 2024
%E A379020 a(1)=5 inserted by _Max Alekseyev_, May 28 2025