Hendrik Lenstra's sixtieth birthdayApril 24, Leiden.
A special day at the occasion of Hendrik Lenstra's sixtieth birthday will be held on April 24 in Leiden. The morning program contains two
mathematical talks and is part of the workshop
Points on Varieties. The afternoon will feature more personal
talks by friends and colleagues of Hendrik Lenstra. Everybody is
welcome to attend.
Morning program in the De Sitterzaal, Oort building:
- 9:15: coffee
- 9:45: opening
- 9:50 - 10:40: Carl Pomerance (Dartmouth)
- 10:50 -11:40: Manjul Bhargava (Princeton)
Afternoon program in the Lorentzzaal (A144)
Kamerlingh Onnes Gebouw, Steenschuur 25, Leiden.
- 14:00 - 14:25: Ed Schaefer (Santa Clara)
- 14:30 - 14:55: Everett Howe (San Diego)
- 15:00: coffee
- 15:30 - 15:55: Johannes Buchmann (Darmstadt)
- 16:00 - 16:25: Richard Groenewegen (London)
- 16:30: closing and drinks
Organisers: Ronald van Luijk, Bart de Smit, Peter Stevenhagen, Lenny Taelman.
|09:50-10:40||Carl Pomerance, Sociable numbers|
Abstract. Consider iterating the function which sends a natural number
to the sum of its proper divisors. A fixed point for this system,
such as 6 or 28, is called perfect, while a number belonging to a
cycle of length 2, such as 220 or 284, is called amicable. Known to
Euclid and Pythagoras, some scholars have even found allusions
to perfect and amicable numbers in the Old Testament. Sociable
numbers are the natural generalization of perfect and amicable
numbers to cycles of arbitrary length - they are mere
youngsters, having been studied for only a century! This talk
will describe the colorful history of the problem (with more
connections to Hendrik Lenstra than you might imagine) and
report on some recent results on the distribution of sociable
numbers within the natural numbers.
|10:50-11:40||Manjul Bhargava, Galois closure for rings|
Abstract. Abstract: We all learn the notion of "Galois closure" or "normal
closure" for a finite extension of fields. But what might we mean by
the "Galois closure" of an extension of rings?
(joint work with Matthew Satriano; based on conversations with Hendrik Lenstra, Jean-Pierre Serre, Bart de Smit, and Kiran Kedlaya)
|14:00-14:25||Ed Schaefer, I started feeling sorry for the problem.|
|14:30-14:55||Everett Howe, Channeling your advisor|
|15:30-15:55||Johannes Buchmann, Hendrik Lenstra and cryptography|
|16:00-16:25||Richard Groenewegen, A sense of reality|