a(n) is the number of binary strings of length n+3 such that there exists a subsequence of length 4 with 2 ones in it.

A118648

a(n) is the number of binary strings of length n+3 such that there exists a subsequence of length 4 with 2 ones in it.

Terms

    a(0) =11a(1) =25a(2) =54a(3) =114a(4) =237a(5) =486a(6) =988a(7) =1998a(8) =4027a(9) =8097a(10) =16253a(11) =32587a(12) =65286a(13) =130727a(14) =261668a(15) =523631a(16) =1047669a(17) =2095900a(18) =4192576a(19) =8386223a(20) =16773924a(21) =33549888a(22) =67102592a(23) =134209071a(24) =268423507a(25) =536854419a(26) =1073719059a(27) =2147452226

External references