Might just go to work like this

SELECT * FROM gallery2 WHERE topic_id="1806489" UNION SELECT * FROM gallery2 WHERE topic_id="512081" UNION SELECT * FROM gallery2 WHERE topic_id="1199243" UNION SELECT * FROM gallery2 WHERE topic_id="1735767" UNION SELECT * FROM gallery2 WHERE topic_id="667162" UNION SELECT * FROM gallery2 WHERE topic_id="643944" UNION SELECT * FROM gallery2 WHERE topic_id="1329232" UNION SELECT * FROM gallery2 WHERE topic_id="571973" UNION SELECT * FROM gallery2 WHERE topic_id="244439" UNION SELECT * FROM gallery2 WHERE topic_id="1014734" UNION SELECT * FROM gallery2 WHERE topic_id="1121393" UNION SELECT * FROM gallery2 WHERE topic_id="1593973" UNION SELECT * FROM gallery2 WHERE topic_id="1066650" UNION SELECT * FROM gallery2 WHERE topic_id="670426" UNION SELECT * FROM gallery2 WHERE topic_id="13348" UNION SELECT * FROM gallery2 WHERE topic_id="1183825"