a(n) = number of n-lettered words in the alphabet {1, 2} with as many occurrences of the substring (consecutive subword) [1, 1] as of [2, 2].

A182027

a(n) = number of n-lettered words in the alphabet {1, 2} with as many occurrences of the substring (consecutive subword) [1, 1] as of [2, 2].

Terms

    a(0) =1a(1) =2a(2) =2a(3) =2a(4) =4a(5) =6a(6) =12a(7) =20a(8) =40a(9) =70a(10) =140a(11) =252a(12) =504a(13) =924a(14) =1848a(15) =3432a(16) =6864a(17) =12870a(18) =25740a(19) =48620a(20) =97240a(21) =184756a(22) =369512a(23) =705432a(24) =1410864a(25) =2704156a(26) =5408312a(27) =10400600a(28) =20801200a(29) =40116600

External references