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Product_{n>=1} 1 / (1 - a(n)*x^n/n!) = 1 + tan(x).
6

%I #6 May 11 2022 10:37:17

%S 1,-2,2,-32,56,-416,3184,-85504,309760,-4087552,48104704,-546922496,

%T 10591523840,-194387924992,3133776259072,-129880886411264,

%U 1249919350046720,-29073986250604544,624022403933077504,-15137719350365519872,381632216575339397120,-11149155036737662615552

%N Product_{n>=1} 1 / (1 - a(n)*x^n/n!) = 1 + tan(x).

%t nn = 22; f[x_] := Product[1/(1 - a[n] x^n/n!), {n, 1, nn}]; sol = SolveAlways[0 == Series[f[x] - 1 - Tan[x], {x, 0, nn}], x]; Table[a[n], {n, 1, nn}] /. sol // Flatten

%Y Cf. A000182, A009006, A353583, A353584, A353611, A353873, A353910, A353912.

%K sign

%O 1,2

%A _Ilya Gutkovskiy_, May 10 2022