Given d1=19d_1 = 19d1=19, d2=20d_2 = 20d2=20, and dn=dn−1+dn−2d_n = d_{n-1} + d_{n-2}dn=dn−1+dn−2 for ngeq3n \\geq 3ngeq3, what is d4d_4d4?
404040
585858
787878
595959