Daniel J. Kleitman (born October 4, 1934)^[1][2][3] is an American mathematician and professor of applied mathematics at MIT. His research interests include combinatorics, graph theory, genomics, and operations research.

Kleitman was born in 1934 in Brooklyn, New York,^[1] the younger of Bertha and Milton Kleitman's two sons. His father was a lawyer who after WWII became a commodities trader and investor. In 1942 the family moved to Morristown, New Jersey,^[4] and he graduated from Morristown High School in 1950.^[1]

Kleitman then attended Cornell University, from which he graduated in 1954,^[1] and received his PhD in Physics from Harvard University in 1958 under Nobel Laureates Julian Schwinger and Roy Glauber.^[5] He is the "k" in G. W. Peck, a pseudonym for a group of six mathematicians that includes Kleitman. Formerly a physics professor at Brandeis University,^[6] Kleitman was encouraged by Paul Erdős to change his field of study to mathematics. Perhaps humorously, Erdős once asked him, "Why are you only a physicist?"^[1]

Kleitman joined the applied mathematics faculty at MIT in 1966, and was promoted to professor in 1969.^[6]

Kleitman coauthored at least six papers with Erdős, giving him an Erdős number of 1.

He was a math advisor and extra for the film Good Will Hunting.^[7] Since Minnie Driver, who appeared in Good Will Hunting, also appeared in Sleepers with Kevin Bacon, Kleitman has a Bacon number of 2. Adding the two numbers results in an Erdős–Bacon number of 3, which is a tie with Bruce Reznick for the lowest number anyone has.^[8]

In 2024 Kleitman was elected as a member of the National Academy of Sciences.^[9]

On July 26, 1964 Kleitman married Sharon Ruth Alexander. They have three children.^[1]

• Kleitman, Daniel (1966). "On a combinatorial problem of Erdős". Proc. Amer. Math. Soc. 17: 139–141. doi:10.1090/s0002-9939-1966-0184866-9. MR 0184866.
• Kleitman, Daniel (1969). "On Dedekind's problem: The number of monotone Boolean functions". Proc. Amer. Math. Soc. 21 (3): 677–682. doi:10.1090/s0002-9939-1969-0241334-6. MR 0241334.
• Kleitman, Daniel; Rothschild, Bruce (1970). "The number of finite topologies". Proc. Amer. Math. Soc. 25 (2): 276–282. doi:10.1090/s0002-9939-1970-0253944-9. MR 0253944.
• Erdős, Paul; Kleitman, Daniel (1971). "On collections of subsets containing 4-member Boolean algebras". Proc. Amer. Math. Soc. 28: 87–90. doi:10.1090/s0002-9939-1971-0270924-9. MR 0270924.
• Kleitman, Daniel J.; Rothschild, Bruce L. (1975). "Asymptotic enumeration of partial orders on a finite set" (PDF). Trans. Amer. Math. Soc. 205: 205–220. doi:10.1090/s0002-9947-1975-0369090-9. MR 0369090.
• Kleitman, Daniel; Markowsky, George (1975). "On Dedekind's problem: The number of isotone Boolean functions. II". Trans. Amer. Math. Soc. 213: 373–390. doi:10.1090/s0002-9947-1975-0382107-0. MR 0382107.
• Kleitman, Daniel J.; Rothschild, Bruce R.; Spencer, Joel H. (1976). "The number of semigroups of order n". Proc. Amer. Math. Soc. 55 (1): 227–232. doi:10.1090/s0002-9939-1976-0414380-0. MR 0414380.^[10]
• Kalai, Gil; Kleitman, Daniel J. (1992). "A quasi-polynomial bound for the diameter of graphs of polyhedra". Bull. Amer. Math. Soc. (N.S.). 26 (2): 315–316. arXiv:math/9204233. doi:10.1090/s0273-0979-1992-00285-9. MR 1130448. S2CID 37821778.
• Alon, Noga; Kleitman, Daniel J. (1992). "Piercing convex sets". Bull. Amer. Math. Soc. (N.S.). 27 (2): 252–256. doi:10.1090/s0273-0979-1992-00304-x. MR 1149871.
• Coventry, Alex; Kleitman, Daniel J.; Berger, Bonnie (2004). "MSARI: Multiple sequence alignments for statistical detection of RNA secondary structure". Proc Natl Acad Sci U S A. 101 (33): 12102–12107. Bibcode:2004PNAS..10112102C. doi:10.1073/pnas.0404193101. PMC 514400. PMID 15304649.

• Kleitman–Wang algorithms
• Littlewood–Offord problem

• Kleitman's homepage
• Peck, G. W. (2002). "Kleitman and Combinatorics: A Celebration". Discrete Mathematics. 257 (2–3): 193–224. doi:10.1016/S0012-365X(02)00595-2. MR 1935723. (article available on Douglas West's web page, University of Illinois at Urbana–Champaign)