From George Gilbert's marks problem: jumping 3 marks at a time (initial positions).

Terms

a(0) =1a(1) =2a(2) =7a(3) =12a(4) =17a(5) =36a(6) =41a(7) =83a(8) =275a(9) =284a(10) =307a(11) =443a(12) =444a(13) =775a(14) =869a(15) =2523a(16) =3485a(17) =4069a(18) =5772a(19) =9689a(20) =16403a(21) =30902a(22) =53359a(23) =83792a(24) =122933a(25) =1090845a(26) =1473689a(27) =1510781a(28) =1740110a(29) =2652867