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 A180417 #19 Apr 19 2023 09:04:22
%S A180417 0,0,1,173,1211969509,5547480986860602794895774677,
%T A180417 708720364531529518355420122993246286974247836241724513772950684967495246261
%N A180417 a(n) = (A000111(2^n) - 1) / 2^n.
%C A180417 The definition yields integers according to the formula in A000111.
%C A180417 The next term a(7) is too large to include. - _N. J. A. Sloane_, Mar 14 2011
%H A180417 Alois P. Heinz, <a href="/A180417/b180417.txt">Table of n, a(n) for n = 0..8</a>
%t A180417 t = Range[0, 65]! CoefficientList[ Series[ Sec@x + Tan@x, {x, 0, 65}], x]; f[n_] := (Rest[t][[2^n]] - 1)/2^n; Array[f, 7, 0] (* _Robert G. Wilson v_, Sep 04 2010 *)
%o A180417 (Python)
%o A180417 from sympy import euler
%o A180417 def A180417(n): return euler(1<<n)-1>>n if n > 1 else 0 # _Chai Wah Wu_, Apr 18 2023
%Y A180417 Cf. A000079, A000111.
%K A180417 nonn
%O A180417 0,4
%A A180417 _Vladimir Shevelev_, Sep 03 2010
%E A180417 Two more terms from _R. J. Mathar_, Sep 19 2010
%E A180417 a(5) and a(6) from _Robert G. Wilson v_, Sep 04 2010