%I #2 Mar 30 2012 18:59:44

%S 18,254,1571,6335,19615,50743,115234,237066,451320,807180,1371293,

%T 2231489,3500861,5322205,7872820,11369668,16074894,22301706,30420615,

%U 40866035,54143243,70835699,91612726

%N The z^2 coefficients of the polynomials in the GF4 denominators of A156933

%C See A157705 for background information.

%F a(n) = 7*a(n-1)-21*a(n-2)+35*a(n-3)-35*a(n-4)+21*a(n-5)-7*a(n-6)+a(n-7)

%F a(n) = 1/2*n^6+5/2*n^5+41/8*n^4+67/12*n^3+27/8*n^2+11/12*n

%F G.f.: (18 + 128*z + 171*z^2 + 42*z^3 + z^4)/(1-z)^7

%p nmax:=23; for n from 0 to nmax do fz(n):=product((1-(2*n+1-2*k)*z)^(3*k+1), k=0..n); c(n):= coeff(fz(n),z,2); end do: a:=n-> c(n): seq(a(n), n=1..nmax);

%Y Cf. A156933, A157705

%K easy,nonn

%O 1,1

%A _Johannes W. Meijer_, Mar 07 2009