IF(OR(NOT(ISNULL(SLA_Date__c)),SLA_Date__c > TODAY()),
TODAY()-SLA_Date__c,
IF(Next_Activity_Date__c >= TODAY(),
0,
IF(AND(ISNULL(Last_Activity_Date__c),
 TODAY()-DATEVALUE(CreatedDate)>5),
TODAY()-DATEVALUE(CreatedDate)-5 ,
((5 * ( FLOOR( ( TODAY() - DATE( 1900, 1, 8) ) / 7 ) ) + MIN( 5, MOD( Last_Activity_Date__c - DATE( 1900, 1, 8), 7 ) ) )
-
(5 * ( FLOOR( ( Last_Activity_Date__c - DATE( 1900, 1, 8) ) / 7 ) ) + MIN( 5, MOD( Last_Activity_Date__c - DATE( 1900, 1, 8), 7 ) ) ) + 1
-
IF(AND(Last_Activity_Date__c <= DATEVALUE("2016-11-24"),TODAY() >= DATEVALUE("2016-11-24")),1,0) -
IF(AND(Last_Activity_Date__c <= DATEVALUE("2016-12-23"),TODAY() >= DATEVALUE("2016-12-23")),1,0) -
IF(AND(Last_Activity_Date__c <= DATEVALUE("2016-12-26"),TODAY() >= DATEVALUE("2016-12-26")),1,0) -
IF(AND(Last_Activity_Date__c <= DATEVALUE("2017-1-2"),TODAY() >= DATEVALUE("2017-1-2")),1,0)-
IF(AND(Last_Activity_Date__c <= DATEVALUE("2017-1-3"),TODAY() >= DATEVALUE("2017-1-3")),1,0)


))))

 formatted table

Formatted :font:(default)calibri,(asian)calibri,complex script font:calibri
 formattted:list paragraph,numbered +level:1 +Numbering style:1,2,3,...+start at:1+ alignment: left+aligned at: 0.25"+indent at 0.5"
Formatted :font:(default)calibri,(asian)calibri,complex script font:calibri
 

these is What i have Written,,

trigger UpdateAccount on Account (after insert,after update, after delete, after undelete) 
{
set<ID> setAccountIDs=new Set<ID>();
for (Account a:Trigger.new)
{
setAccountIDs.add(a.AccountID);
List <Account> accounts=[select ID,Name from Account Where ID IN: setAccountIDs];
String accName = '';
a.name=accName;
}
update account;
}