Number of compositions of 7*n into parts 2 and 7.

Terms

a(0) =1a(1) =1a(2) =2a(3) =9a(4) =38a(5) =136a(6) =452a(7) =1495a(8) =5031a(9) =17114a(10) =58282a(11) =198032a(12) =671856a(13) =2278870a(14) =7731892a(15) =26238839a(16) =89047335a(17) =302191369a(18) =1025487338a(19) =3479970844a(20) =11809261583a(21) =40074827170a(22) =135994407483a(23) =461498426696