Number of strings of length n over a 4-letter alphabet that begin with a nontrivial palindrome.

A249629

Number of strings of length n over a 4-letter alphabet that begin with a nontrivial palindrome.

Terms

    a(0) =0a(1) =0a(2) =4a(3) =28a(4) =124a(5) =532a(6) =2164a(7) =8788a(8) =35284a(9) =141628a(10) =567004a(11) =2269948a(12) =9081724a(13) =36334492a(14) =145345564a(15) =581412508a(16) =2325680284a(17) =9302841652a(18) =37211487124a(19) =148846430068a(20) =595386201844

External references