OFFSET
1,3
COMMENTS
Symmetric strings of -1, 0, and 1, including as many leading as trailing zeros.
LINKS
Lei Zhou, Table of n, a(n) for n = 1..10000
EXAMPLE
10 is included since in balanced ternary notation 10 = (101)_bt is a palindrome;
144 is included since 144 = (1TT100)_bt, where we use T to represent -1. When trailing zeros removed, 1TT1 is a palindrome.
MATHEMATICA
BTDigits[m_Integer, g_] :=
Module[{n = m, d, sign, t = g},
If[n != 0, If[n > 0, sign = 1, sign = -1; n = -n];
d = Ceiling[Log[3, n]]; If[3^d - n <= ((3^d - 1)/2), d++];
While[Length[t] < d, PrependTo[t, 0]]; t[[Length[t] + 1 - d]] = sign;
t = BTDigits[sign*(n - 3^(d - 1)), t]]; t];
BTpaleQ[n_Integer] := Module[{t, trim = n/3^IntegerExponent[n, 3]},
t = BTDigits[trim, {0}]; t == Reverse[t]];
Select[Range[0, 363], BTpaleQ[#] &]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Lei Zhou, Dec 13 2013
STATUS
approved