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These are Bell numbers, A000110. The relatively explicit formula given in the Encyclopedia: $$a_n=\frac{2n!}{\pi e}\Im\left(\int_{0}^{\pi} e^{e^{e^{ix}}} \sin(nx) dx \right)$$
These are Bell numbers, A000110. The relatively explicit formula given in the Encyclopedia: $$a_n=\frac{2n!}{\pi e}\Im\left(\int_{0}^{\pi} e^{e^{e^{ix}}} \sin(nx) dx \right)$$
