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 A062624 #30 Nov 27 2024 07:27:01 %S A062624 1,1,1,4,6,12,40,240,480,1920,6912,20736,76032,253440,608256,4257792, %T A062624 7983360,26611200,88704000,319334400,1277337600,5109350400, %U A062624 19508428800,73156608000,336520396800,1177821388800,6281714073600,23332080844800,66663088128000 %N A062624 Number of integers less than A000108(n) relatively prime to A000108(n). %H A062624 Harry J. Smith, <a href="/A062624/b062624.txt">Table of n, a(n) for n = 0..200</a> %H A062624 Florian Luca and Pantelimon Stanica, <a href="https://doi.org/10.1016/j.jnt.2012.02.002">On the Euler function of the Catalan numbers</a>, Journal of Number Theory, Vol. 132, No. 7 (2012), pp. 1404-1424. %F A062624 a(n) = phi(binomial(2n, n)/(n+1)). %F A062624 a(n) = A000010(A000108(n)). %p A062624 with(numtheory): a:= n-> phi(binomial(2*n,n)/(n+1)): seq(a(n), n=0..27); # _Zerinvary Lajos_, Oct 05 2007 %t A062624 a[n_] := EulerPhi[CatalanNumber[n]]; Array[a, 30, 0] (* _Amiram Eldar_, Nov 27 2024 *) %o A062624 (PARI) a(n) = eulerphi(binomial(2*n, n)/(n + 1)); %o A062624 (Sage) [euler_phi(binomial(2*n,n)/(n+1))for n in range(0,28)] # _Zerinvary Lajos_, Jun 06 2009 %Y A062624 Cf. A000010, A000108. %K A062624 easy,nonn %O A062624 0,4 %A A062624 _Jason Earls_, Jul 04 2001