Let us denote the sum by S:
S=log2(1+11)+log2(1+21)+⋯+log2(1+20141)
We have:
log2(1+k1)=log2(kk+1)=log2(k+1)−log2k
Therefore,
S=k=1∑2014[log2(k+1)−log2k]
This is a telescoping sum:
S=log22−log21+log23−log22+log24−log23+⋯+log22015−log22014
All terms except the first log22 and the last −log22014 cancel, so:
S=log2(2015)−log21=log2(2015)
We need to show that log2(2015)<11.
But 211=2048>2015, so log2(2015)<11.
Therefore,
log2(1+11)+log2(1+21)+⋯+log2(1+20141)<11.