Ramsey Number R(5,5) and other Ramsey Number Values

[franzhusch]

What is the conjecture

The Ramsey number $R(5,5)$ is defined as the smallest positive integer $n$ such that every 2-coloring of the edges of the complete graph $K_n$ contains either a monochromatic clique of 5 vertices or a monochromatic independent set of 5 vertices. Equivalently, for any graph $G$ on $n$ vertices, either $G$ or its complement $\overline{G}$ contains a clique of size 5. The exact value of $R(5,5)$ remains unknown, but it is bounded: $43 \leq R(5,5) \leq 48$.

Also add conjectures for other small values.

(This description may contain subtle errors especially on more complex problems; for exact details, refer to the sources.)

Sources:

• https://oeis.org/A212954, https://mathworld.wolfram.com/RamseyNumber.html, https://gilkalai.wordpress.com/2017/03/29/r55-%E2%89%A4-48/, https://ajc.maths.uq.edu.au/pdf/5/ocr-ajc-v5-p13.pdf, https://math.mit.edu/~apost/courses/18.204_2018/ramsey-numbers.pdf

Prerequisites needed

Formalizability Rating: 1/5 (0 is best) (as of 2026-02-19)

Building blocks (from search results):

• SimpleGraph and complete graphs from Mathlib.Combinatorics.SimpleGraph
• Graph coloring definitions and 2-coloring concepts
• Cliques and independent sets in SimpleGraph theory

Missing pieces:

• Formal definition of Ramsey number as a minimum function for this specific case
• Lean statements of the established bounds (43 ≤ R(5,5) ≤ 48)

Rating justification: The core graph-theoretic concepts needed to state the conjecture are available in Mathlib. Formalizing the statement primarily requires packaging existing definitions (complete graphs, colorings, cliques, independent sets) into a statement about the Ramsey number bounds; no major new foundational infrastructure is needed.

AMS categories

• ams-05

Choose either option

• I plan on adding this conjecture to the repository
• This issue is up for grabs: I would like to see this conjecture added by somebody else

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