Sample text:
<a href="http://test.com/sam1/666_XY.jpg"></a><a href="http://test.com/sam2/1001_A.jpg"></a><a href="http://test.com/sam3/1002_A.jpg"></a><a href="http://test.com/sam4/1003_A.jpg"></a>

RegExp:
<a href=\"http:\/\/test.com\/(.*?)\/((?:(?!XY).)*?)_A\.jpg\"><\/a>

Needed:
1001, 1002, 1003