We present a long term light curve (LC) of the flat spectrum radio quasar (FSRQ) 4C +21.35 (also known as PKS 1222+216, z=0.432) observed by the Fermi Large Area Telescope (LAT) during the first seven years of the mission with weekly time binning in the energy range 0.2–50 GeV. The highest weekly integral flux was reached on MJD = 55365 (2010, Jun. 18). The variability of the source emission was studied with 12 hour time binning in two energy bands 0.2 – 0.8 GeV and 0.8 – 50 GeV. Three different statistical methods, the structure functions (SF), auto-correlation functions (ACF), and fast fourier transformer were used to study the time scales. For the 7 year-weekly binning light curve, 18 week time scale was observed. Flare I seems to have the same time scales for both energy ranges as well. Therefore the outbursts during flare I may come from the same emission mechanism/s, CCF between the two energy bands have also emphasized it. Flare II did not give significant results, CCF illustrated 6.5 day time lag that indicates the emission mechanism of the low energy band came before the high energy one with 6.5 day with a typical physical process.