Number of compositions of n avoiding three consecutive parts in arithmetic progression.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =7a(5) =13a(6) =22a(7) =42a(8) =81a(9) =149a(10) =278a(11) =516a(12) =971a(13) =1812a(14) =3374a(15) =6297a(16) =11770a(17) =21970a(18) =41002a(19) =76523a(20) =142901a(21) =266779a(22) =497957a(23) =929563a(24) =1735418a(25) =3239698a(26) =6047738a(27) =11289791a(28) =21076118a(29) =39344992