puzzle - Formula to this pattern? $1$, $11$, $21$, $1211$, $111221

next 1221Virtual channel 15.1, Cox 1011, Spectrum 1221. Use the TV schedules pages as a TV guide for KPBS, KPBS2, KPBS Create, and PBS Kids.Angel number 1221 is a combination of the energies and vibrations of number 1 and number 2, with the number 2 appearing twice, amplifying its influence. Number 1 represents