I think I can get one more term... %S A000001 1,2,4,18,56,272,1000,6080,33644,214024,1363836,10877964,75783376, %T A000001 648644300,5765475224,49406530846 %N A000001 Number of permutations of 1..n with no three elements collinear %O A000001 1,2 It grows a lot slower than n! . --- rhhardin at mindspring.com rhhardin at att.net (either)