The difference between A089580(n) and A089579(n).

Terms

a(0) =0a(1) =4a(2) =10a(3) =20a(4) =41a(5) =65a(6) =114a(7) =185a(8) =297a(9) =487a(10) =809a(11) =1339a(12) =2253a(13) =3824a(14) =6544a(15) =11297a(16) =19620a(17) =34216a(18) =59926a(19) =105258a(20) =185356a(21) =327039a(22) =577906a(23) =1022466a(24) =1810789a(25) =3209398a(26) =5691825a(27) =10099475a(28) =17927609a(29) =31833805