IMO Shortlist 1974 problem 6
Dodao/la:
arhiva2. travnja 2012. Prove that for any n natural, the number
cannot be divided by

.
%V0
Prove that for any n natural, the number $$\sum \limits_{k=0}^{n} \binom{2n+1}{2k+1} 2^{3k}$$
cannot be divided by $5$.
Izvor: Međunarodna matematička olimpijada, shortlist 1974