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 A065549 #68 May 11 2020 03:56:19
%S A065549 2,4,8,64,256,512,32768,1073741824,17592186044416,9007199254740992,
%T A065549 9223372036854775808,
%U A065549 1852673427797059126777135760139006525652319754650249024631321344126610074238976
%N A065549 a(1) = 1; for n > 1, a(n) = 2^((A000043(n) - 1)/2).
%C A065549 Proper subset of A065405.
%C A065549 These values also relate to the sequence of perfect numbers. Every even perfect number except 6 can be written as Sum_{k=1..a(n)} (2*k-1)^3. - _Derek Orr_, Sep 28 2013
%C A065549 Positive real roots of 2n^4 - n^2 - A000396(n) = 0 for A000396(n) > 6. - _César Aguilera_, Nov 11 2018
%H A065549 Muniru A Asiru, <a href="/A065549/b065549.txt">Table of n, a(n) for n = 2..20</a>
%F A065549 log(n) is approximately log(sqrt(A000668(n)/2)). - _César Aguilera_, Nov 11 2018
%t A065549 Array[2^((MersennePrimeExponent@ # - 1)/2) &, 12, 2] (* _Michael De Vlieger_, Aug 25 2018 *)
%o A065549 (PARI) lista(nn) = {forprime(p=3, nn, if (isprime(2^p-1), print1(2^((p-1)/2), ", ")););} \\ _Michel Marcus_, Aug 04 2016
%Y A065549 Cf. A000043, A065403, A065404, A065405, A000396.
%K A065549 nonn
%O A065549 2,1
%A A065549 _Labos Elemer_, Nov 13 2001