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 A103478 #22 Dec 22 2018 16:38:48 %S A103478 5,23,73,125,1945,23471 %N A103478 Positive integers k for which 1 + 5*2^(k+2) divides the Fermat number 1 + 2^2^k. %C A103478 On Keller's linked page, to find the terms, you run through the tables and find all rows with k = 5 and with n exactly 2 greater than m, then that m belongs to this sequence. - _Jeppe Stig Nielsen_, Dec 04 2018 %H A103478 Wilfrid Keller, <a href="http://www.prothsearch.com/fermat.html">Prime factors k*2^n + 1 of Fermat numbers F_m</a> %e A103478 a(1)=5 because 5 is the smallest positive integer k for which 1 + 5*2^(k+2) divides the Fermat number 1 + 2^2^k. %t A103478 Select[Range[1, 2000], Mod[1 + PowerMod[2, 2^#, 1 + 5*2^(# + 2)], 1 + 5*2^(# + 2)] == 0 &] (* _Julien Kluge_, Jul 08 2016 *) %o A103478 (PARI) isok(n) = Mod(2, 1+5*2^(n+2))^(2^n) + 1 == 0; \\ _Michel Marcus_, Apr 29 2016 %Y A103478 Cf. A000215, A083575, A103477, A103479. %K A103478 nonn,more,hard %O A103478 1,1 %A A103478 Serhat Sevki Dincer (mesti_mudam(AT)yahoo.com), Feb 07 2005