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A073963
Number of strings of length n over Z_5 with trace 0 and subtrace 0.
7
1, 1, 1, 25, 125, 625, 3025, 15625, 78625, 393125, 1955625, 9765625, 48815625, 244140625, 1220703125, 6103515625, 30517265625, 152587890625, 762941015625, 3814705078125, 19073494140625, 95367431640625, 476837119140625, 2384185791015625, 11920928955078125
OFFSET
1,4
COMMENTS
Same as the number of strings of length n over GF(5) with trace 0 and subtrace 0.
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*(525*x^6-525*x^5+190*x^4-26*x^2+9*x-1) / ((5*x-1)*(5*x^2-1)*(25*x^4-25*x^3+15*x^2-5*x+1)). - Colin Barker, Apr 03 2015
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