Not true; it always takes four, no matter how many recusals there are.
With 2 recusals only takes 3 according to Kerchner:
http://puzo1.blogspot.com/2010/11/obama-ineligible-obama-i-tried-and-lied.html
U.S. Supreme Court orders were posted at 10:00 a.m. on 29 Nov 2010. See below. Certiorari for our case was denied. The two justices appointed by Obama who had in my opinion a direct financial conflict of interest (their very jobs and appointments to the court) in the outcome of this petition and case did not recuse themselves even though they should have! Their recusal was called for in our petition on page 36 with relevant U.S. Code cited. The two justices and the court ignored that. There were recusals declared by these two Obama appointees in many other petitions including the one immediately before our petition in the orders list and the one immediately after. Imo, apparently the court needed all nine justices in the room to kill the petition. With the full court of 9 justices it’s the rule/vote of 4 to grant certiorari to move the case forward. With two recusals that would have left only 7 justices and it’s then the rule/vote of 3 to grant certiorari to move the case forward. I suspect the water cooler buzz at SCOTUS was that 3 justices were leaning for granting certiorari. So it looks like Sotomayer and Kagan ignored ethical considerations and stayed in the review of the petition to be sure it got killed, i.e., to be in that room to argue against Certiorari, and to require 4 votes to grant cert instead of 3 ... financial conflict of interest and ethics be damned by those two justices. JMHO.