a(n) = (17 - 3*(-1)^n)/2.

Terms

a(0) =7a(1) =10a(2) =7a(3) =10a(4) =7a(5) =10a(6) =7a(7) =10a(8) =7a(9) =10a(10) =7a(11) =10a(12) =7a(13) =10a(14) =7a(15) =10a(16) =7a(17) =10a(18) =7a(19) =10a(20) =7a(21) =10a(22) =7a(23) =10a(24) =7a(25) =10a(26) =7a(27) =10a(28) =7a(29) =10