Number of permutations of [n] with no 3-term arithmetic progression.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =20a(6) =48a(7) =104a(8) =282a(9) =496a(10) =1066a(11) =2460a(12) =6128a(13) =12840a(14) =29380a(15) =74904a(16) =212728a(17) =368016a(18) =659296a(19) =1371056a(20) =2937136a(21) =6637232a(22) =15616616a(23) =38431556a(24) =96547832a(25) =198410168a(26) =419141312a(27) =941812088a(28) =2181990978a(29) =5624657008