Using Christian Krattenthaler's hyp.q tells you the following - the important information is at the end, and the result agrees with Johannes' comment.

    In[1]:= <<hyp.m
    
    Out[1]= ▒
    
    In[10]:= S = SUM[1/(n+1/2)*(Gamma[n]^2/Gamma[n+1/2]^2),{n,1,Infinity}]
    
             Infinity
              -----                2
               \           Gamma[n]
    Out[10]=    >    ---------------------
               /      1            1     2
              -----  (- + n) Gamma[- + n]
               n=1    2            2
    
    In[19]:= SF = S/.SUMF
    
                  [ 1, 1, 1    ]
                  |            |      2
             2  F |  5  3  ; 1 | Ga(1)
               3 2|  -, -      |
                  [  2  2      ]
    Out[19]= --------------------------
                           3 2
                      3 Ga(-)
                           2
    
    In[21]:= SF/.SListe
    
    Be sure to apply "FOrdne" before using the following information!
    
                            2
               2 S3261 Ga(1)
    Out[21]= {{--------------}}
                       3 2
                  3 Ga(-)
                       2
    
    In[22]:= SF/.S3261
    
                             1     1     1   3                              3    1     1     1   3
                         [ -(-), -(-), -(-), - ]      [   1     1     ]   [ -, -(-), -(-), -(-), - ]
                    2    |   2     2     2   2 |      | -(-), -(-)    |   | 2    2     2     2   2 |
             2 Ga(1)  (Ga|                     | -  F |   2     2 ; 1 | Ga|                        |)
                         |      3   1  1  1    |   2 1|               |   |      3                 |
                         [    -(-), -, -, -    ]      [     0         ]   [    -(-), 1, 1, 1, 0    ]
                                2   2  2  2                                      2
    Out[22]= ----------------------------------------------------------------------------------------
                                                          3 2
                                                     3 Ga(-)
                                                          2
    
    In[23]:= SF/.S3261/.SListe
    
    Be sure to apply "FOrdne" before using the following information!
    
                               1     1     1   3               3    1     1     1   3
                           [ -(-), -(-), -(-), - ]           [ -, -(-), -(-), -(-), - ]
                      2    |   2     2     2   2 |           | 2    2     2     2   2 |
               2 Ga(1)  (Ga|                     | - S2103 Ga|                        |)
                           |      3   1  1  1    |           |      3                 |
                           [    -(-), -, -, -    ]           [    -(-), 1, 1, 1, 0    ]
                                  2   2  2  2                       2
    Out[23]= {{-------------------------------------------------------------------------}}
                                                    3 2
                                               3 Ga(-)
                                                    2
    
    In[33]:= R = SF/.S3261/.S2103/.Gzerl
    
                            1  3    3            1  3    3 2
                       Ga(-(-))  Ga(-)      Ga(-(-))  Ga(-)
                    2       2       2            2       2
             2 Ga(1)  (--------------- - ----------------------)
                            3      1 3        3      1 2      2
                       Ga(-(-)) Ga(-)    Ga(-(-)) Ga(-)  Ga(1)
                            2      2          2      2
    Out[33]= ---------------------------------------------------
                                       3 2
                                  3 Ga(-)
                                       2
    
    In[42]:= Simplify[R]
    
                    1  3       2      1     3
             2 Ga(-(-))  (Ga(1)  - Ga(-) Ga(-))
                    2                 2     2
    Out[42]= ----------------------------------
                         3      1 3    3
                  3 Ga(-(-)) Ga(-)  Ga(-)
                         2      2      2
    
    In[52]:= ?S3261
    Summation formula (Slater, Appendix (III.31)) in form of a rule.
    
    In[53]:= ?S2103
    Summation formula (Slater, Appendix (III.3)) in form of a rule.