From May 20th, 2019, according to the ISO standard, the Planck constant, h = 6.62607015*10^(-34) J*s, is exact and is one of the seven 1990 SI units (see the BIPM link and
A322415). Since the Avogadro constant N_A = 6.02214076*10^23 mol^(-1) is also exact according to the same standard system, it follows that the last term of the present sequence is a(17) = 4.