Number of nonempty subsequences {s(k)} of 1..n such that the difference sequence is palindromic.

Terms

a(0) =1a(1) =3a(2) =7a(3) =13a(4) =23a(5) =37a(6) =59a(7) =89a(8) =135a(9) =197a(10) =291a(11) =417a(12) =607a(13) =861a(14) =1243a(15) =1753a(16) =2519a(17) =3541a(18) =5075a(19) =7121a(20) =10191a(21) =14285a(22) =20427a(23) =28617a(24) =40903a(25) =57285a(26) =81859a(27) =114625a(28) =163775a(29) =229309