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  _____     _____     _  __    ______   _    _   
 /  ___||  |  ___||  | |/ //  /_   _// | \  / || 
| // __    | ||__    | ' //    -| ||-  |  \/  || 
| \\_\ ||  | ||__    | . \\    _| ||_  | .  . || 
 \____//   |_____||  |_|\_\\  /_____// |_|\/|_|| 
  `---`    `-----`   `-` --`  `-----`  `-`  `-`

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發送短信 : Ramanujan's convolution sum twisted by Dirichlet characters