He completed an S.B. and S.M. in Mathematics at the Massachusetts Institute of Technology in 1972. The title of his thesis was "Evaluation of certain character sums". He was a Putnam Fellow at MIT in 1970. He received his Ph.D. in Mathematics from MIT for his thesis "The 4-part of the class group of a quadratic field", in 1974. His advisor for both his masters and Ph.D was Harold Stark.
In 1975 he joined AT&T Bell Laboratories and eventually became Distinguished Member of Technical Staff. Since 1995, he has been a Technology Consultant at AT&T Research Laboratories. In 2002, he moved to Michigan to work at the University and settle down with his family.
While his recent work has been in theoretical computer science, his original training was in analytic algebraic number theory. He has since worked in many areas, both pure and applied, and considers himself a mathematical generalist. Lagarias discovered an elementary problem that is equivalent to the Riemann hypothesis, namely whether for all n > 0, we have
with equality only when n = 1. Here Hn is the nth harmonic number, the sum of the reciprocals of the first positive integers, and σ(n) is the divisor function, the sum of the positive divisors of n. He disproved Keller's conjecture in dimensions at least 10. Lagarias has also done work on the Collatz conjecture and Li's criterion and has written several highly cited papers in symbolic computation with Dave Bayer.
Awards and honors
- "Jeffrey C. Lagarias" (PDF). CV.
- "Jeffrey Lagarias, Professor". University of Michigan.
- "The 3x + 1 Problem and Its Generalizations". Amer. Math. Monthly. 92: 3–23. 1985.
- "Wild and Wooley Numbers". Amer. Math. Monthly. 113: 97–106. 2006. doi:10.2307/27641862.
- List of Fellows of the American Mathematical Society, retrieved 2013-01-27.