Re: Numbers problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg19533] Re: [mg19520] Numbers problem*From*: Hans Havermann <haver at total.net>*Date*: Tue, 31 Aug 1999 00:52:23 -0400*Sender*: owner-wri-mathgroup at wolfram.com

It's called "Langford's Problem". It first appeared around 1958 and was popularized by Martin Gardner ten years later. Here are the number of *pairs* of solutions: 3: 1 4: 1 7: 26 8: 150 11: 17,792 12: 108,144 15: 39,809,640 16: 326,721,800 19: 256,814,891,280 20: ? The case for n = 19 was just solved a few months ago: It took 4 people two months of computing! See: http://www.lclark.edu/~miller/langford.html