Question Given a $t-(v,k,\lambda)$ design $(X,\mathcal{B})$ and a set $U\subset X$ with $|U|=u\leq t$, what is the number of blocks $B\in\mathcal{B}$ such that $B\cap U=\emptyset$? …

This is probably well-known... but I am afraid the literature on this subject bewilders me a little bit: Suppose we have a partial Steiner triple system, whereby I mean a finit …

With parameters: srg(v(v-1)/6, 3(v-3)/2, (v-3)/2, 9) Should be straightforward counting which alludes me... Thanks! Shay

The short version of my question is: 1)For which positive integers $k, n$ is there a solution to the equation $$k(6k+1)=1+q+q^2+\cdots+q^n$$ with $q$ a prime power? 2) For …

Can anyone point me to an online database of Steiner triple systems? My Google-fu is only getting me to descriptions of the few smallest ones, mostly Google book scans (which are …

A Steiner triple system is a decomposition of $K_n$ into $K_3$, such as $S=\{013,026,045,124,156,235,346\}$. Steiner triple systems give rise to a Steiner Latin squares, such as $ …