OFFSET
1,2
COMMENTS
A chiral row is different from its reverse.
LINKS
Index entries for linear recurrences with constant coefficients, signature (6,6,-36).
FORMULA
EXAMPLE
For a(2)=15, the chiral pairs are the fifteen combinations of six colors taken two at a time, e.g., AB-BA.
MATHEMATICA
k = 6; Table[(k^n - k^Ceiling[n/2])/2, {n, 1, 30}]
LinearRecurrence[{6, 6, -36}, {0, 15, 90}, 30]
PROG
(Magma) [(6^n - 6^Ceiling(n / 2)) / 2: n in [1..25]]; // Vincenzo Librandi, Oct 15 2018
(PARI) m=40; v=concat([0, 15, 90], vector(m-3)); for(n=4, m, v[n] = 6*v[n-1] +6*v[n-2] -36*v[n-3]); v \\ G. C. Greubel, Oct 17 2018
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Robert A. Russell, Oct 14 2018
STATUS
approved