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 A013606 #24 Sep 01 2019 11:01:07 %S A013606 1,3,3,5,3,3,3,15,5,3,3,3,5,57,35,5,41,5,45,87,11,17,21,59,27,47,33,5, %T A013606 27,93,57,59,5,23,35,93,35,15,11,65,57,35,35,299,33,83,3,17,51,15,33, %U A013606 17,117,59,21,75,11,3,5,119,3,59,137,159,5,347,45,113,105,27,111 %N A013606 a(n) = 4^n - prevprime(4^n). %H A013606 Daniel Starodubtsev, <a href="/A013606/b013606.txt">Table of n, a(n) for n = 1..1000</a> %F A013606 a(n) = A000302(n) - A104089(n). - _Michel Marcus_, Sep 01 2019 %p A013606 seq(4^i-prevprime(4^i),i=1..100); %t A013606 #-NextPrime[#,-1]&/@(4^Range[80]) (* _Harvey P. Dale_, Dec 13 2016 *) %o A013606 (PARI) a(n) = 4^n - precprime(4^n); \\ _Michel Marcus_, Sep 01 2019 %Y A013606 Cf. A000302, A104089. %K A013606 nonn %O A013606 1,2 %A A013606 James Kilfiger (mapdn(AT)csv.warwick.ac.uk)