Number of solutions to Langford (or Langford-Skolem) problem (up to reversal of the order).
0, 0, 1, 1, 0, 0, 26, 150, 0, 0, 17792, 108144, 0, 0, 39809640, 326721800, 0, 0
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Mon Sep 26 18:28:28 CEST 2011 [seqfan] Re: broken links to pages from W. Schneider