Put TI-89 in approximate mode.

:gamma(x)
:Func
Local z,gamma
If x<1 Then
1-x -> z
Else
x-1 -> z
EndIf
:ˆ(2* ¼)*(z+5.5)^(z+.5)*s^(
-z-5.5)*(1+76.18009173/(z
+1)-86.50532033/(z+2)+24.
01409822/(z+3)-1.23173951
6/(z+4)+.00120858003/(z+5
)-5.36382E-6/(z+6)) -> gamma
:
:If x<1 Then
:If (1-x)* ¼ -> z
:z/gamma/(sin(zr)) -> gamma
:EndIf
:
:If gamma‚undef and gamma‚ƒ 
:round(gamma,10)
EndFunc

sin(zr)  makes sin(z) in radian mode.  r is small from catalog
=================
Bessel Function
n = integer = order of be function
lim = big number=30

Define be(x,n,lim) = …((-1)^k / (k!*gamma(n+k+1))
*(x/2)^(n+2*k),k,0,lim)

be(2.5,1,30) =  .497094102525
be(2.5,0,30) =   

Find zeros of be function
solve(be,1,30)=0,x)|x>1

8 minute wait on TI-89 Titanium

Results
x=3.83170597039 or x=7.01 x= 10.17 or x=13.32 or x=16.47 or x=19.35 or x=19.61 or x=22.76 or x=24.53



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