a(n) is the number of squares at distance n from the central square of a golden square fractal.

Terms

a(0) =1a(1) =4a(2) =12a(3) =28a(4) =60a(5) =132a(6) =300a(7) =692a(8) =1596a(9) =3668a(10) =8412a(11) =19284a(12) =44220a(13) =101428a(14) =232668a(15) =533716a(16) =1224252a(17) =2808180a(18) =6441372a(19) =14775188a(20) =33891324a(21) =77739956a(22) =178319964a(23) =409030356a(24) =938233788a(25) =2152120564a(26) =4936534044a(27) =11323421716a(28) =25973664636a(29) =59578391604