The original question is:

 (4+x^2)y'' + 3xy' + y = 0

The guessed solution is y = \sum_{n=0}^\infty a_n x^nAfter some calculation, I have reduced everything to a single infinite sum plus some terms involving some terms of the sequence.

As for my recurrence relation for the sequence, here are the equations I have found:

8a_2 + a_0 = 0

24a_3 + 4a_1 = 0

a_n = \frac {4(n+2)a_{n+2}}{n+1}<br />

So what do I do now to find the general formula for the sequence of coefficients?