%I #9 Jun 19 2024 23:45:55
%S 1,6,21,79,296,1117,4237,16147,61782,237208,913466,3526826,13647886,
%T 52920075,205566205,799791235,3116196550,12157265980,47485135510,
%U 185671296850,726703966600,2846827216330,11161555459090,43794648931054
%N a(n) = A026626(2*n, n-1).
%H G. C. Greubel, <a href="/A026628/b026628.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = ( (357*n^4 - 1625*n^3 + 2157*n^2 - 841*n + 60)*a(n-1) + 2*(2*n-5)*(51*n^3 - 101*n^2 + 34*n + 6)*a(n-2) )/(2*(n+1)*(51*n^3 - 254*n^2 + 389*n - 180)), for n >= 3, with a(1) = 1, a(2) = 6. - _G. C. Greubel_, Jun 19 2024
%t a[n_]:= a[n]= If[n<3, 5*n-4, ((357*n^4 -1625*n^3 +2157*n^2 -841*n +60 )*a[n-1] +2*(2*n-5)*(51*n^3 -101*n^2 +34*n +6)*a[n-2])/(2*(n+1)*(51*n^3 -254*n^2 +389*n -180))];
%t Table[a[n], {n,41}]
%o (Magma)
%o [n le 2 select 5*n-4 else ((357*n^4-1625*n^3+2157*n^2-841*n+60)*Self(n-1) +2*(2*n-5)*(51*n^3-101*n^2+34*n+6)*Self(n-2))/(2*(n+1)*(51*n^3-254*n^2+389*n-180)): n in [1..41]]; // _G. C. Greubel_, Jun 19 2024
%o (SageMath)
%o @CachedFunction
%o def a(n): # a = A026628
%o if n<3: return 5*n-4
%o else: return ((357*n^4 -1625*n^3 +2157*n^2 -841*n +60)*a(n-1) +2*(2*n-5)*(51*n^3 -101*n^2 +34*n +6)*a(n-2))/(2*(n+1)*(51*n^3-254*n^2+389*n-180))
%o [a(n) for n in range(1,41)] # _G. C. Greubel_, Jun 19 2024
%Y Cf. A026626, A026627, A026629, A026630, A026631, A026632, A026633.
%Y Cf. A026634, A026635, A026636, A026961, A026962, A026963, A026964.
%Y Cf. A026965.
%K nonn
%O 1,2
%A _Clark Kimberling_