Mally sequence
 

It is well known that there are infinite sequences of IMPOSSIBLE prime
factors of exponential functions of the type a^n+c where a belongs to N and is fixed, n is a variable belonging to N and c belongs to Z.(The only exception is 2^n-1 which has only 2 as an impossible factor.(For an
example see seq A123239 of OEIS).

Polynomials also have infinite sequences of IMPOSSIBLE prime factors
and x^2 + x + 97 (x belongs to N) has the following infinite sequence
of I.factors:

2,5,19...........

Let me call this a Mally sequence ( in honour of late Mally).
A.K.Devaraj