We prove that (j,k)=(2019,1010) is a valid solution. More generally, let p(x) be the polynomial of degree N such that p(2n+1)=F2n+1 for 0≤n≤N. We will show that p(2N+3)=F2N+3−FN+2.
Define a sequence of polynomials p0(x),…,pN(x) by p0(x)=p(x) and pk(x)=pk−1(x)−pk−1(x+2) for k≥1. Then by induction on k, it is the case that pk(2n+1)=F2n+1+k for 0≤n≤N−k, and also that pk has degree (at most) N−k for k≥1. Thus pN(x)=FN+1 since pN(1)=FN+1 and pN is constant.
We now claim that for 0≤k≤N, pN−k(2k+3)=∑j=0kFN+1+j. We prove this again by induction on k: for the induction step, we have pN−k(2k+3)=pN−k(2k+1)+pN−k+1(2k+1)=FN+1+k+j=0∑k−1FN+1+j. Thus we have p(2N+3)=p0(2N+3)=∑j=0NFN+1+j.
Now one final induction shows that ∑j=1mFj=Fm+2−1, and so p(2N+3)=F2N+3−FN+2, as claimed. In the case N=1008, we thus have p(2019)=F2019−F1010.