Asymptotics of Lagged Fibonacci Sequences

Consider “lagged” Fibonacci sequences $a(n)=a(n-1)+a(\lfloor n\mathrm{/}k\rfloor )$ for $k>1$. We show that ${\lim }_{n\to \mathrm{\infty }}a(kn)\mathrm{/}a(n)\cdot \ln n\mathrm{/}n=k\ln k$ and we demonstrate the slow numerical convergence to this limit and how to deal with this slow convergence. We also discuss the connection between two classical results of N.G. de Bruijn and K. Mahler on the asymptotics of $a(n)$.