Let Bn be the set of all sequences of length n, consisting of zeros and ones. For every two sequences a,b∈Bn (not necessarily different) we define strings ε0ε1ε2…εn and δ0δ1δ2…δn such that ε0=δ0=0 and
\varepsilon_{i+1}=(\delta_i-a_{i+1})(\delta_i-b_{i+1}), \delta_{i+1}=\delta_i+(-1)^{\delta_i}\varepsilon_{i+1} (0 \leq i \leq n-1).
. Let w(a,b)=ε0+ε1+ε2+⋯+εn . Find f(n)=a,b∈Bn∑w(a,b).
. SequenceStringsSumcombinatorics