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