Number of ways to toss a coin n times and not get a run of four.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =14a(5) =26a(6) =48a(7) =88a(8) =162a(9) =298a(10) =548a(11) =1008a(12) =1854a(13) =3410a(14) =6272a(15) =11536a(16) =21218a(17) =39026a(18) =71780a(19) =132024a(20) =242830a(21) =446634a(22) =821488a(23) =1510952a(24) =2779074a(25) =5111514a(26) =9401540a(27) =17292128a(28) =31805182a(29) =58498850