It is easy to derive that hn=nn(2n+1)2(n+1)n+1. Consider the function g(x) defined by:
g(x)=ln2+(x+1)ln(x+1)−xlnx−ln(2x+1)
Then, for 0<x<+∞, we have
g′(x)=ln(x+1)−lnx−2x+12g′′(x)=x+11−x1+(2x+1)24=−x(x+1)(2x+1)21<0
Therefore, g′(x) is monotonically decreasing on (0,+∞).
Since limx→∞g′(x)=limx→∞lnxx+1−limx→∞2x+12=0, and knowing that g′(x) is positive on (0,+∞), it follows that g(x) is monotonically increasing on (0,+∞). Therefore, when n is a positive integer, hn=eg(n) is a strictly increasing sequence, i.e., h1<h2<⋯<hn<hn+1.