var that = [];
$( '#a1,#a2,#a3').one('click', function(){
  that[$(this).index()] = $(this);
  c_down($(this).index());
} );
var c_down = function(index){  
  num =  that[index].data('num')-0;
  if( num> 0 ){
    num --;
    that[index].text('已发送'+ num).data( 'num', num );   
   setTimeout( 'c_down('+index+')', 1000 );
  }else{
  	num =60;    
    that[index].text('重新发送').data( 'num', num ).one('click',function(){c_down( $(this).index() )}); 
  }
  }