Number of states in the evolutionary spatial prisoner's dilemma with n players.

Terms

a(0) =2a(1) =2a(2) =2a(3) =3a(4) =4a(5) =6a(6) =9a(7) =13a(8) =19a(9) =28a(10) =42a(11) =63a(12) =95a(13) =143a(14) =216a(15) =327a(16) =496a(17) =754a(18) =1147a(19) =1747a(20) =2662a(21) =4059a(22) =6192a(23) =9450a(24) =14428a(25) =22034a(26) =33658a(27) =51422a(28) =78573a(29) =120073