OFFSET
1,3
COMMENTS
Same as the number of strings of length n over Z_5 with: trace 2 and subtrace 4, trace 3 and subtrace 4, or trace 4 and subtrace 1.
Same as the number of strings of length n over GF(5) with: trace 1 and subtrace 1, trace 2 and subtrace 4, trace 3 and subtrace 4, or trace 4 and subtrace 1.
LINKS
FORMULA
a(n; t, s) = a(n-1; t, s) + a(n-1; t+4, s+4t+1) + a(n-1; t+3, s+3t+4) + a(n-1; t+2, s+2t+4) + a(n-1; t+1, s+t+1).
Empirical g.f.: -x^3*(25*x^4+75*x^3-85*x^2+35*x-6) / ((5*x-1)*(5*x^2-1)*(25*x^4-25*x^3+15*x^2-5*x+1)). - Colin Barker, Nov 26 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Frank Ruskey and Nate Kube, Aug 15 2002
EXTENSIONS
Terms a(11) onward from Max Alekseyev, Apr 09 2013
STATUS
approved