Question

正项级数(1!+2!+……+n!)/(2n)!的敛散性

Answer 1

令Un=(1!+2!+……+n!)/(2n)!,U(n+1)=(1!+2!+……+n!+(n+1)!)/(2n+2)!,U(n+1)/Un=1/(2n+2)*(2n+1)+(n+1)!/(2n+2)*(2n+1)*(1!+2!+……+n!)/当n趋于无穷大时U(n+1)/Un趋于零（比式判别法的极限形式）即得证