1-5-9 is the second offical single to be released by Fremantle unit Koi Child. The band consists of Blake Hart on drums, Tom Kenny on Keys, Yann Vissac on Bass, Christian Ruggiero on tenor sax, Jamie Canney on alto sax, Sam Newman on trombone and Shannon Cruz on vocals . This 7 piece come together to create a jazz-funk banger with Nas-esque rhymes and a psychedelic tinge from producer and engineer Kevin Parker.

1-5-9 are the numbers corresponding to the respective notes in an E minor scale that are played in the bass line. The first three notes of the bass line phrase are E-A-F#, and E is the first note in the scale, A is the fifth note in the scale, and the F# is the second note in the scale but in a higher octave, which is commonly referred to as the ninth note in the scale–hence the name 1-5-9.