Expansion of 1/(1-4x-4x^3).

Terms

a(0) =1a(1) =4a(2) =16a(3) =68a(4) =288a(5) =1216a(6) =5136a(7) =21696a(8) =91648a(9) =387136a(10) =1635328a(11) =6907904a(12) =29180160a(13) =123261952a(14) =520679424a(15) =2199438336a(16) =9290801152a(17) =39245922304a(18) =165781442560a(19) =700288974848