Largest prime factor of 9^n - 4^n.
5, 13, 19, 97, 211, 61, 463, 401, 1009, 4621, 35839, 5521, 29927, 369181, 3571, 14177, 129009091, 1009, 745181, 4621, 92233, 2414250301, 2002867877, 41432641, 39756701, 13761229, 397760329, 3001769, 68629840493971, 24001, 617671248800299, 1607133116929
1
Note that these numbers can be factored into (3^n - 2^n)*(3^n + 2^n). Hence, the largest prime factor is about the square root of similar sequences 9^n - m^n for m not equal to 4.
T. D. Noe, Plot of 100 terms
T. D. Noe, Table of 100 terms
Eric W. Weisstein, MathWorld: Greatest Prime Factor
(Mma) Table[FactorInteger[9^n - 4^n][[-1, 1]], {n, 40}]
nonn
T. D. Noe, Jun 08 2015