Rudresh Mahanthappa is most often hailed in the press for combining avant-garde jazz with Indian classical music, but his 2004 album Mother Tongue was also inspired by language. On Codebook, the alto saxophonist and his quartet (piano, drums, and bass) explore the connections between jazz, cryptography, and number theory. “The Decider,” the leadoff track, features a warped melody line ostensibly inspired by the Fibonacci sequence of integers, but the title also alludes to President Bush’s mangled wordplay. “Play It Again Sam,” a piece dedicated to Samuel Morse, begins and ends with a string of musical dots and dashes, a kind of Morse code message set through music. On “Frontburner,” Mahanthappa draws from John Coltrane’s experiments with Indian music while his equally impressive pianist-collaborator Vijay Iyer evokes the spirit of Thelonious Monk. Considering the complicated concept underlying Codebook, the music is surprisingly accessible in spite of its melodic and harmonic sophistication.