Jagadguru Rambhadracharya composed the epic in 2002 at Chitrakuta during his sixth six-month Payovrata (milk-only diet).[3] The poet chose 21 as the number of cantos due to several reasons. He composed the epic at the beginning of the 21st century, and it was the first Sanskrit epic to be composed in the 21st century. The number 21 is also associated with the narrative of the epic. Reṇukā, the mother of Paraśurāma, beats her chest 21 times after the Haihaya kings murder her husband Jamadagni. Subsequently, Paraśurāma annihilates the Kṣatriyas 21 times from the earth.
Source: Sribhargavaraghaviyam – Wikipedia
Tim B.
https://en.wikipedia.org/wiki/Rambhadracharya