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

A248122

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

Terms

    a(0) =0a(1) =0a(2) =3a(3) =15a(4) =51a(5) =165a(6) =507a(7) =1551a(8) =4683a(9) =14127a(10) =42459a(11) =127599a(12) =383019a(13) =1149693a(14) =3449715a(15) =10351023a(16) =31054947a(17) =93170397a(18) =279516747a(19) =838566831a(20) =2515717083a(21) =7547200797a(22) =22641651939a(23) =67925104239a(24) =203775461139a(25) =611326828047

External references