A012212 Number of squarefree palindromes over {0, 1, 2} of length 2n+1.

3, 6, 6, 12, 12, 12, 12, 18, 18, 24, 36, 48, 60, 84, 102, 138, 186, 246, 306, 378, 486, 630, 816, 1050, 1350, 1782, 2328, 2988, 3870, 5076, 6624, 8616, 11112, 14454, 18882, 24630, 31944, 41442, 53988, 70422, 91614, 119046, 154896, 201834, 262824, 341688

Offset

0,1

Links

Giovanni Resta, Table of n, a(n) for n = 0..55

Mathematica

s = {"1", "2", "3"}; L=s; a={3}; ext[w_] := Select[#<>w<># & /@ s, StringFreeQ[#, x__ ~~ x__] &]; Do[L = Flatten[ext /@ L, 1]; AppendTo[a, Length@ L], {30}]; a (* Giovanni Resta, Aug 26 2018 *)

Crossrefs

Cf. A006156.

Sequence in context: A066297 A160713 A279625 * A232941 A080866 A310131

Adjacent sequences: A012209 A012210 A012211 * A012213 A012214 A012215

Keyword

nonn,base

Author

Jeffrey Shallit

Extensions

a(31)-a(45) from Giovanni Resta, Aug 26 2018

Status

approved