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 A056743 #3 Mar 30 2012 17:30:26
%S A056743 0,1,2,6,18,176,630,7710,27594,356960,18407808,69273666,3697909056,
%T A056743 53630700752,204064589160,2992477516800,169917983040000,
%U A056743 9770466930024800,37800705069076950,2202596295934991760
%N A056743 a(n) = phi(2^prime(n) - 1)/prime(n); a(0) = 0 by convention.
%p A056743 with numtheory; A056743 := proc(n) phi( 2^ithprime(n) - 1 )/ithprime(n); end;
%t A056743 Phi( A001348) / A000040. Table[EulerPhi[(2^Prime[n] - 1)]/Prime[n], {n, 1, 25}]
%Y A056743 Cf. A000020, A064535.
%K A056743 nonn
%O A056743 0,3
%A A056743 _Robert G. Wilson v_, Aug 14 2000