Ramsey Number

The Ramsey number gives the solution to the party problem, which asks the minimum number of guests that must be invited so that at least will know each other or at least will not know each other. In the language of graph theory, the Ramsey number is the minimum number of vertices such that all undirected simple graphs of order contain a clique of order or an independent set of order . Ramsey's theorem states that such a number exists for all and .

By symmetry, it is true that

(1)

It also must be true that

(2)

A generalized Ramsey number is written

(3)

and is the smallest integer such that, no matter how each -element subset of an -element set is colored with colors, there exists an such that there is a subset of size , all of whose -element subsets are color . The usual Ramsey numbers are then equivalent to .

Bounds are given by

(4)

and

(5)

(Chung and Grinstead 1983). Erdős proved that for diagonal Ramsey numbers ,

(6)

This result was subsequently improved by a factor of 2 by Spencer (1975). was known since 1980 to be bounded from above by , and Griggs (1983) showed that was an acceptable limit. J.-H. Kim (Cipra 1995) subsequently bounded by a similar expression from below, so

(7)

Burr (1983) gives Ramsey numbers for all 113 graphs with no more than 6 graph edges and no isolated points.

A summary of known results up to 1983 for is given in Chung and Grinstead (1983). Radziszowski (2004) maintains an up-to-date list of the best current bounds. Results from Tables I and II of Radziszowski (2004) are reproduced below in a slightly less cramped format than in the original. Known bounds for generalized Ramsey numbers (multicolor graph numbers), hypergraph Ramsey numbers, and many other types of Ramsey numbers may be found in Radziszowski (2004). In the absence of a published upper bound, the theorem of Erdős-Szekeres stating that is used to provide one.

			Reference
3	3	6	Greenwood and Gleason 1955
3	4	9	Greenwood and Gleason 1955
3	5	14	Greenwood and Gleason 1955
3	6	18	Graver and Yackel 1968
3	7	23	Kalbfleisch 1966
3	8	28	McKay and Min 1992
3	9	36	Grinstead and Roberts 1982
3	10	[40, 43]	Exoo 1989c, Radziszowski and Kreher 1988
3	11	[46, 51]	Radziszowski and Kreher 1988
3	12	[52, 59]	Exoo 1993, Radziszowski and Kreher 1988, Exoo 1998, Lesser 2001
3	13	[59, 69]	Piwakowski 1996, Radziszowski and Kreher 1988
3	14	[66, 78]	Exoo (unpub.), Radziszowski and Kreher 1988
3	15	[73, 88]	Wang and Wang 1989, Radziszowski (unpub.), Lesser 2001
3	16	[79, 135]	Wang and Wang 1989
3	17	[92, 152]	Wang et al. 1994
3	18	[98, 170]	Wang et al. 1994
3	19	[106, 189]	Wang et al. 1994
3	20	[109, 209]	Wang et al. 1994
3	21	[122, 230]	Wang et al. 1994
3	22	[125, 252]	Wang et al. 1994
3	23	[136, 275]	Wang et al. 1994
4	4	18	Greenwood and Gleason 1955
4	5	25	McKay and Radziszowski 1995
4	6	[35, 41]	Exoo (unpub.), McKay and Radziszowski 1995
4	7	[49, 61]	Exoo 1989a, Mackey 1994
4	8	[56, 84]	Exoo 1998, Exoo 2002
4	9	[73, 115]	Radziszowski 1988, Mackey 1994
4	10	[92, 149]	Piwakowski 1996, Mackey 1994, Harboth and Krause 2003
4	11	[97, 191]	Piwakowski 1996, Spencer 1994, Burr et al. 1989
4	12	[128, 238]	Su et al. 1998, Spencer 1994
4	13	[133, 291]	Xu and Xie 2002
4	14	[141, 349]	Xu and Xie 2002
4	15	[153, 417]	Xu and Xie 2002
4	16	[153, 815]
4	17	[182, 968]	Luo et al. 2001
4	18	[182, 1139]
4	19	[198, 1329]	Luo et al. 2002
4	20	[230, 1539]	Su et al. 1999
4	21	[242, 1770]	Su et al. 1999
4	22	[282, 2023]	Su et al. 1999
5	5	[43, 49]	Exoo 1989b, McKay and Radziszowski 1995
5	6	[58, 87]	Exoo 1993, Walker 1971
5	7	[80, 143]	CET, Spencer 1994
5	8	[101, 216]	Piwakowski 1996, Spencer 1994, Harborth and Krause 2003
5	9	[125, 316]	Exoo 1998, Haanpää 2000
5	10	[143, 442]	Exoo 1998, Mackey 1994
5	11	[157, 1000]	Exoo 1998, Xiaodong et al. 2004
5	12	[181, 1364]	Exoo 1998
5	13	[205, 1819]	Exoo 1998, Xiaodong et al. 2004
5	14	[233, 2379]	Exoo 1998, Xiaodong et al. 2004
5	15	[261, 3059]	Su et al. 2002, Xiaodong et al. 2004
5	16	[278, 3875]	Luo et al. 2001
5	17	[284, 4844]	Exoo 2002
5	18	[284, 5984]
5	19	[338, 7314]	Su et al. 1999
5	20	[380, 8854]	Luo et al. 2001
5	21	[380, 10625]
5	22	[422, 12649]	Luo et al. 2000
5	23	[434, 14949]	Luo et al. 2000
5	24	[434, 17549]
5	25	[434, 20474]
5	26	[464, 23750]
6	6	[102, 165]	Kalbfleisch 1965, Mackey 1994
6	7	[113, 298]	Exoo 1998, Xu and Xie 2002
6	8	[127, 495]	Exoo 1998, Xu and Xie 2002
6	9	[169, 780]	Exoo 1998, Mackey 1994, Xiaodong et al. 2004
6	10	[179, 1171]	Xu and Xie 2002
6	11	[253, 3002]	Xu and Xie 2002
6	12	[262, 4367]	Xu and Xie 2002
6	13	[317, 6187]	Xu and Xie 2002, Xiaodong et al. 2004
6	14	[317, 8567]	Xu and Xie 2002
6	15	[401, 11627]	Su et al. 2002, Xiaodong et al. 2004
6	16	[434, 15503]	Su et al. 2002
6	17	[548, 20348]	Su et al. 2002
6	18	[614, 26333]	Su et al. 2002
6	19	[710, 33648]	Su et al. 2002
6	20	[878, 42503]	Su et al. 2002
6	21	[878, 53129]
6	22	[1070, 65779]	Su et al. 2002
7	7	[205, 540]	Hill and Irving 1982, Giraud 1973
7	8	[216, 1031]	Xu and Xie 2002
7	9	[233, 1713]	Huang and Zhang 1998, Xiaodong and Zheng 2002
7	10	[232, 2826]	Mackey 1994
7	11	[405, 8007]	Xu and Xie 2002, Xiaodong and Zheng 2002
7	12	[416, 12375]	Xu and Xie 2002
7	13	[511, 18563]	Xu and Xie 2002
7	14	[511, 27131]
7	15	[511, 38759]
7	16	[511, 54263]
7	17	[628, 74612]	Xu and Xie 2002
7	18	[722, 100946]	Xu and Xie 2002
7	19	[908, 134595]	Su et al. 2002
7	20	[908, 177099]
7	21	[1214, 230229]	Su et al. 2002
8	8	[282, 1870]	Burling and Reyner 1972, Mackey 1994
8	9	[317, 3583]	Radziszowski 2002, Xiaodong et al. 2004
8	10	[377, 6090]	Xu and Xie 2002, Huang and Zhang 1998, Xiaodong et al. 2004
8	11	[377, 19447]
8	12	[377, 31823]
8	13	[817, 50387]	Xu and Xie 2002, Xiaodong et al. 2004
8	14	[817, 77519]
8	15	[861, 116279]	Xu and Xie 2002, Xiaodong et al. 2004
8	16	[861, 170543]
8	17	[861, 245156]	Xu and Xie 2002
8	18	[871, 346103]	Xu and Xie 2002
8	19	[1054, 480699]	Xu and Xie 2002
8	20	[1094, 657799]	Su et al. 2002
8	21	[1328, 888029]	Su et al. 2002
9	9	[565, 6588]	Shearer 1986, Shi and Zheng 2001
9	10	[580, 12677]	Xu and Xie 2002
10	10	[798, 23556]	Shearer 1986, Shi 2002
11	11	[1597, 184755]	Mathon 1987
12	12	[1637, 705431]	Xu and Xie 2002
13	13	[2557, 2704155]	Mathon 1987
14	14	[2989, 10400599]	Mathon 1987
15	15	[5485, 40116599]	Mathon 1987
16	16	[5605, 155117519]	Mathon 1987
17	17	[8917, 601080389]	Luo et al. 2002
18	18	[11005, 2333606219]	Luo et al. 2002
19	19	[17885, 9075135299]	Luo et al. 2002