Row Numbering (First four of same number assigned 1, remaining of number assigned 10000)

[krector]

Hi Guys,

Bit of a weird scenario here that I haven't run into before. Basically I have a sorted item number in column A and need to assign a family number in column B. The first four rows of a given item number get the family numbers starting from 1, with the remaining rows of that number assigned a family number starting at 10000. The number of rows each item number appears varies but basically i need to come up with a formula or macro to number the first for "1" and the reaming "10,000" increasing by 1 for each new item number.

Item Number Family Number
6033383 1
6033383 1
6033383 1
6033383 1
6033383 10001
6033383 10001
6033383 10001
7384938 2
7384938 2
7384938 2
7384938 2
7384938 10002
2893726 3
2893726 3
2893726 3
2893726 3
2893726 10003
2893726 10003
1328938 =??????????
1328938 =??????????

[FDibbins]

See if this is what you want...
=IF(A2=A1,IF(COUNTIF($A$2:A2,A2)=5,10000+C1,C1),IF(ISNUMBER(C1),--RIGHT(C1,3)+1,1))