24 C.F.R. § 203.409
Debentures shall, at the option of the Commissioner and with the approval of the Secretary of the Treasury, be redeemable at par plus accrued interest on any semiannual interest payment date on three months' notice of redemption given in such manner as the Commissioner shall prescribe. The debenture interest on the debentures called for redemption shall cease on the semiannual interest payment date designated in the call notice. The Commissioner may include with the notice of redemption an offer to purchase the debentures at par plus accrued interest at any time during the period between the notice of redemption and the redemption date. If the debentures are purchased by the Commissioner after such call and prior to the named redemption date, the debenture interest shall cease on the date of purchase.
24 C.F.R. §203.409