Sheikh Sa`d al-Shuwayrikh
It is related in the Sunnah to make three rows for the funeral prayer. The Prophet (peace be upon him) said: “Whoever dies and three rows of Muslims pray for him, then he will be entitled to good” [Sunan Abî Dâwûd and Sunan al-Tirmidhî]
For this reason, Imam Mâlik used to divide people into three rows for the funeral prayer.
However, if having three rows is not practical, then we need not endeavor for some other odd number. We prefer three rows because it was explicitly stated in Sunnah, but the Sunnah never mentions odd numbers in general.
And Allah knows best.
Source: Islam Today