Revenue Ruling 2015-21 provides various prescribed rates for October 2015, including the applicable federal interest rates, the adjusted applicable federal interest rates, the adjusted federal long-term rate, and the adjusted federal long-term tax-exempt rate.  These rates are determined as prescribed by section 1274.  The rates are published monthly for purposes of sections 42, 382, 412, 1288, 1274, 7520, 7872, and various other sections of the Internal Revenue Code.