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BIBD problem, combinatorics

How many different (7,7,3,3,1) BIBD are there on vertex set[7]? Note that two such designs are different if their sets of blocks are different. That is, we do not require that the BIBDs be ...
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block design question combinatorics

Let D be a BIBD with parameters (b,v,r,3,1). Prove that either v=6i+1 or v=6i+3 for some non-negative integer i. BIBD stands for a Balanced Incomplete Block Design My work, theorem states that bk=vr ...