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Number of compositions of 5*n into parts 1 and 5.
8

%I #16 Mar 15 2024 17:39:43

%S 1,2,8,34,140,571,2328,9496,38740,158045,644761,2630364,10730820,

%T 43777405,178594110,728591751,2972359720,12126025705,49469281395,

%U 201814663875,823322219501,3358821723401,13702634402876,55901207340276,228054320813276,930369409108152

%N Number of compositions of 5*n into parts 1 and 5.

%H Paolo Xausa, <a href="/A369836/b369836.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (6,-10,10,-5,1).

%F a(n) = A003520(5*n).

%F a(n) = Sum_{k=0..n} binomial(n+4*k,n-k).

%F a(n) = 6*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5).

%F G.f.: (1-x)^4/((1-x)^5 - x).

%t LinearRecurrence[{6, -10, 10, -5, 1}, {1, 2, 8, 34, 140}, 50] (* _Paolo Xausa_, Mar 15 2024 *)

%o (PARI) a(n) = sum(k=0, n, binomial(n+4*k, n-k));

%Y Cf. A079675, A369837, A369838, A369839.

%Y Cf. A099131, A369840, A369845.

%Y Cf. A003520.

%K nonn

%O 0,2

%A _Seiichi Manyama_, Feb 03 2024