Backward iterated ( limited ) Fibonacci approximation: A000045.

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =19a(5) =32a(6) =52a(7) =85a(8) =139a(9) =225a(10) =365a(11) =592a(12) =958a(13) =1551a(14) =2511a(15) =4064a(16) =6577a(17) =10642a(18) =17220a(19) =27863a(20) =45084a(21) =72948a(22) =118033a(23) =190982a(24) =309016