no. 2
The automorphism group of the modular curve X 0 (63)
Compositio Mathematica, Tome 74 (1990) no. 2, pp. 203-208. 
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     author = {Elkies, Noam D.},
     title = {The automorphism group of the modular curve $X_0(63)$},
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     volume = {74},
     number = {2},
     year = {1990},
     mrnumber = {1047740},
     zbl = {0708.14016},
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     url = {http://www.numdam.org/item/CM_1990__74_2_203_0/}
}
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Elkies, Noam D. The automorphism group of the modular curve $X_0(63)$. Compositio Mathematica, Tome 74 (1990) no. 2, pp. 203-208. http://www.numdam.org/item/CM_1990__74_2_203_0/

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