等差数列{a n}中，a 2+a 10+a 12为定值，则{a n}中的前n项和一定为常数的是

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='13509' and id < 1097192 and id<>'1097192' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='13509' and id > 1097192 and id<>'1097192' order by id asc limit 5