Question: HeunB function expansion

I want to series expand the HeunB function. But I am facing some problems with this. please help. Here is the given HeunB function. 

HB1 := HeunB(5/2, -5^(1/4)*(2*M - R)/sqrt((2*M - R)*(4*M - R)), (17*sqrt(5))/10, (3*5^(3/4)*(2*M - R))/(2*sqrt((2*M - R)*(4*M - R))), 5^(1/4)*sqrt((2*M - R)*(4*M - R))*r^2/(2*(2*M - R)*R^2))

 

Here M, R are arbitrary constants.

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