Execute a JS/jQuery function on focus

I have some jQuery that I need to execute onFocus for the datepicker which will block out days.

Here's the jQuery that I'm running on the page:

<script>
function disableDays(selector,days,min) {
    var $ = jQuery;    
    var daysToDisable = days; // [5, 6] // Sat & Sun   

    function disableSpecificWeekDays(date) {        
        var day = date.getDay();        
        for (i = 0; i < daysToDisable.length; i++) {          
            if ($.inArray(day, daysToDisable) != -1) {            
                return [false];          
            }        
        }        
        return [true];      
    }

    $(selector).datepicker('option', 'beforeShowDay', disableSpecificWeekDays);
    $(selector).datepicker('option', 'minDate', min);
}
</script>

I need to execute this function on focus for Field ID 75

How do I add this to the datepicker input?
onfocus='(disableDays('#input_2_75',[5,6],'+4d');):"

Thanks Richard,

I got it working...

For anyone else.... Here's what I did...

Script above and:

<script>
jQuery('#input_2_75').one('focus',function() {
  disableDays('#input_2_75',[0,6],'+4d')
});
</script>