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 A371238 #8 Mar 16 2024 04:19:43
%S A371238 2,6,8,20,24,32,36,84,96,80,108,96,144,120,128,324,320,288,420,336,
%T A371238 360,476,384,512,432,560,540,504,632,480,600,1364,960,1344,1296,1536,
%U A371238 1440,1296,1584,1296,1772,1512,1280,1760,1440,1980,1800,1600,1800,2016,1536,1872
%N A371238 Euler totient function applied to the binary palindromes of even length.
%H A371238 Amiram Eldar, <a href="/A371238/b371238.txt">Table of n, a(n) for n = 1..10000</a>
%H A371238 William D. Banks and Igor E. Shparlinski, <a href="http://dx.doi.org/10.4064/ba54-2-1">Average value of the Euler function on binary palindromes</a>, Bulletin of the Polish Academy of Sciences, Mathematics, Vol. 54, No. 2 (2006), pp. 95-101; <a href="https://eudml.org/doc/286495">alternative link</a>.
%F A371238 a(n) = A000010(A048701(n)).
%F A371238 (1/N(k)) * Sum_{j, A070939(A048701(j)) = 2*k} a(j) = 3 * 2^(2*k-2) * (6/Pi^2 + O((k/log(k))^(-1/4))), where N(k) = Sum_{j, A070939(A048701(j)) = 2*k} 1 (Banks and Shparlinski, 2006).
%t A371238 EulerPhi[Select[Range[5000], EvenQ[Length[(d = IntegerDigits[#, 2])]] && PalindromeQ[d] &]]
%o A371238 (PARI) is(n) = Vecrev(n = binary(n)) == n && !((#n)%2);
%o A371238 lista(kmax) = for(k = 1, kmax, if(is(k), print1(eulerphi(k), ", ")));
%Y A371238 Cf. A000010, A006995, A048701, A059956, A070939.
%K A371238 nonn,base,easy
%O A371238 1,1
%A A371238 _Amiram Eldar_, Mar 16 2024