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 A383030 #7 Apr 13 2025 16:32:32
%S A383030 2,5,7,8,11,16,18,19,22,24,26,29,31,33,35,39,41,43,46,48,51,54,56,58,
%T A383030 61,63,67,69,72,74,76,79,82,84,86,87,91,93,96,98,100,103,106,109,110,
%U A383030 113,115,119,121,122,124,126,129,131,133,136,139,144,147,149,152
%N A383030 Indices of the even terms in the sequence of exponentially odd numbers.
%C A383030 The asymptotic density of this sequence is 2/5.
%H A383030 Amiram Eldar, <a href="/A383030/b383030.txt">Table of n, a(n) for n = 1..10000</a>
%F A383030 A383029(a(n)) > 0.
%t A383030 expOddQ[n_] := AllTrue[FactorInteger[n][[;; , 2]], OddQ]; Position[Select[Range[350], expOddQ], _?EvenQ] // Flatten
%o A383030 (PARI) isexpodd(n) = {my(f = factor(n)); for(i=1, #f~, if(!(f[i, 2] % 2), return (0))); 1;}
%o A383030 list(lim) = {my(c = 0); for(k = 1, lim, if(isexpodd(k), c++; if(!(k % 2), print1(c, ", "))));}
%Y A383030 Cf. A268335, A376218, A383029, A383031.
%K A383030 nonn,easy
%O A383030 1,1
%A A383030 _Amiram Eldar_, Apr 13 2025