Is bank robbery a Class C felony under section 3559(a)(3) of the Criminal Code and, if so, what is the maximum term of imprisonment for the crime?

18 U.S.C. 3559 classifies criminal offenses by letter grade according to the maximum term of imprisonment authorized. See 18 U.S.C. 3559(a). Without regard to its letter grade, the maximum term of imprisonment of an offense "is the term authorized by the law describing the offense." 18 U.S.C. 3559(b) (emphasis added); see United States v. Schiffbauer, No. 90-10624, slip op. at 1081, 1085 (9th Cir. Feb. 4, 1992). Section 2113(a), which describes the offense of bank robbery, clearly states that the maximum term of imprisonment for the offense is 20 years. 18 U.S.C. 2113(a). Therefore, although section 2113(a) does not classify bank robbery by letter grade and by definition is a Class C felony under section 3559(a)(3), the sentencing provisions under 18 U.S.C. 3581(b) are inapplicable. See Schiffbauer, slip op. at 1086.