Covering designs
C(75,17,2) ≤ 26
The smallest known (75,17,2) covering design uses 26 blocks, one fewer than the 27 known before. Quantavane published it on 22 October 2026. The Schönheim bound shows that at least 23 blocks are needed, so C(75,17,2) lies between 23 and 26.
Franco Atzeni reached the same size independently and uploaded it to coveringrepository.com first, on 24 October 2026, so the table lists that upload.
The record
| Ours | 26 blocks |
|---|---|
| Previous best | 27 blocks |
| Previous source | the La Jolla Covering Repository's final data (Daniel M. Gordon, CC BY 4.0), from a general construction |
| Published | 22 October 2026 |
| Status | Franco Atzeni reached the same size independently and uploaded it to coveringrepository.com first, on 24 October 2026, so the table lists that upload. |
| Check | Checked exhaustively by three independent programs; verify.py in the public repository checks it again with plain Python. |
Every pair of the 75 points lies in at least one of the 26 blocks of 17 points.
How it was found and checked
Found by a compiled local search that alternates simulated annealing with breakout weighting. Checked exhaustively by three independent programs; verify.py in the public repository checks it again with plain Python.
git clone https://github.com/arhancanli/quantavane-covering-records
cd quantavane-covering-records
python3 verify.pyTake v points and blocks of k points each. A (v,k,t) covering design is a set of blocks such that every group of t points sits inside at least one block. C(v,k,t) is the fewest blocks that can do it. For most sizes no one knows the exact answer, so public tables keep the best covering anyone has found. Beating an entry means building a valid covering with fewer blocks.
Questions
What is C(75,17,2)?
The fewest blocks of 17 points, drawn from 75 points, such that every pair of points lies in some block.
Is 26 the smallest possible?
Not known. The Schönheim bound gives at least 23; 26 is the smallest covering found so far.
What was the best known before?
27 blocks: the La Jolla Covering Repository's final data (Daniel M. Gordon, CC BY 4.0), from a general construction.