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 A343557 #36 Sep 06 2024 15:16:28 %S A343557 2,3,7,55,116,6543,10847,23974,27567,76709,177975,457523,887643, %T A343557 1625567,2751966,3772007,9385401,42401669,61136051,301137372, %U A343557 2946723445,7632981296,24728168164,98261951745,99582868271,159657063059,231641062432,851793186025,870658222248 %N A343557 Indices of the prime factors of Fermat numbers in the sequence of primes. %H A343557 Amiram Eldar, <a href="/A343557/b343557.txt">Table of n, a(n) for n = 1..50</a> %H A343557 <a href="/index/Pri">Index entries for sequences that are related to primes dividing Fermat numbers</a>. %F A343557 a(n) = A000720(A023394(n)). %F A343557 A000040(a(n)) = A023394(n). %e A343557 A000040(a(5)) = A000040(116) = 641 = A023394(5). %p A343557 q:=n->(irem(2^(2^padic:-ordp(ithprime(n)-1, 2))-1, ithprime(n)) = 0): %p A343557 select(q, [$1..10^5])[]; # _Lorenzo Sauras Altuzarra_, Feb 20 2023 %o A343557 (PARI) is_a023394(p)=p>2 && Mod(2,p)^lift(Mod(2,znorder(Mod(2,p)))^p)==1 && isprime(p) \\ after _Charles R Greathouse IV_ in A023394 %o A343557 my(i=1); forprime(p=1, , if(is_a023394(p), print1(i, ", ")); i++) \\ _Felix Fröhlich_, Apr 30 2021 %Y A343557 Cf. A000040 (primes), A000720 (primepi), A023394 (prime factors of Fermat primes). %Y A343557 Supersequence of A159611. %K A343557 nonn %O A343557 1,1 %A A343557 _Lorenzo Sauras Altuzarra_, Apr 28 2021 %E A343557 More terms from _Michel Marcus_, Apr 29 2021 %E A343557 More terms from _Amiram Eldar_, Apr 29 2021