Number of subsets of {1, ..., n} with no four terms in arithmetic progression.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =15a(5) =29a(6) =56a(7) =103a(8) =192a(9) =364a(10) =668a(11) =1222a(12) =2233a(13) =3987a(14) =7138a(15) =12903a(16) =22601a(17) =40200a(18) =71583a(19) =125184a(20) =218693a(21) =386543a(22) =670989a(23) =1164385a(24) =2021678a(25) =3462265a(26) =5930954a(27) =10189081a(28) =17266616a(29) =29654738