OFFSET
4,2
REFERENCES
F. J. MacWilliams and N. J. A. Sloane, The Theory of Error-Correcting Codes, Elsevier-North Holland, 1978, p. 698.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 4..200
FORMULA
a(n) = Product_{i=1..4} (7^(n-i+1)-1)/(7^i-1), by definition. - Vincenzo Librandi, Aug 06 2016
G.f.: x^4/((1 - x)*(1 - 7*x)*(1 - 49*x)*(1 - 343*x)*(1 - 2401*x)). - Ilya Gutkovskiy, Aug 06 2016
MATHEMATICA
Table[QBinomial[n, 4, 7], {n, 4, 20}] (* Vincenzo Librandi, Aug 06 2016 *)
PROG
(Sage) [gaussian_binomial(n, 4, 7) for n in range(4, 15)] # Zerinvary Lajos, May 27 2009
(Magma) r:=4; q:=7; [&*[(1-q^(n-i+1))/(1-q^i): i in [1..r]]: n in [r..20]]; // Vincenzo Librandi, Aug 06 2016
(PARI) r=4; q=7; for(n=r, 30, print1(prod(j=1, r, (1-q^(n-j+1))/(1-q^j)), ", ")) \\ G. C. Greubel, Jun 13 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset changed by Vincenzo Librandi, Aug 06 2016
STATUS
approved