A221859 - OEIS

%I #18 Apr 02 2024 11:39:17

%S 1,4,15,56,209,779,2898,10760,39882,147612,545721,2015721,7440251,

%T 27448008,101217076,373128151,1375167467,5067236766,18669118971,

%U 68774597447,253334948791,933111590565,3436767111783,12657552835178,46616152422035,171677402416052

%N Expansion of (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).

%C A diagonal of the square array A223968.

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (9,-28,35,-15,1).

%F a(n) = A223968(n,n+2).

%F G.f.: (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).

%F a(n) = 9*a(n-1) - 28*a(n-2) + 35*a(n-3) - 15*a(n-4) + a(n-5) with a(0) = 1, a(1) = 4, a(2) = 15, a(3) = 56, a(4) = 209.

%Y Cf. A223968

%K nonn,easy

%O 0,2

%A _Philippe Deléham_, Apr 10 2013