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 A080309 #4 Mar 30 2012 17:27:18 %S A080309 3,5,6,9,10,12,15,17,24,25,27,30,33,34,39,40,42,45,48,50,51,60,63,65, %T A080309 66,68,69,70,72,75,78,80,81,95,96,111,119,120,123,125,126,129,130,132, %U A080309 135,136,144,159,160,174,175,177,180,183,185,186,187,189,190,192,195,204 %N A080309 n-th even number equals n-th multiple of a Fermat number. %C A080309 Sequence includes only multiples of Fermat numbers (sequence A080307), but not all of them. It is not certain that A080309 is infinite, but it seems likely given that exactly one-half of all integers are multiples of Fermat numbers (see A080307). %e A080309 The first 3 even numbers are 2, 4 and 6; the first 3 multiples of Fermat numbers (the numbers of the form 2^(2^n)+1) are 3, 5 and 6. The third even number is also the third Fermat multiple; thus 3 is in the sequence. %Y A080309 Cf. A000215 (the Fermat numbers), A080307. %K A080309 nonn %O A080309 1,1 %A A080309 _Matthew Vandermast_, Feb 16 2003