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a(n) = (3*n-2)!!! * Sum_{k=0..n} 1/(3*k-2)!!!.
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%I #8 Jan 06 2024 09:22:08

%S 1,2,9,64,641,8334,133345,2533556,55738233,1393455826,39016763129,

%T 1209519657000,41123668338001,1521575728506038,60863029140241521,

%U 2617110253030385404,120387071639397728585,5898966510330488700666,306746258537185412434633

%N a(n) = (3*n-2)!!! * Sum_{k=0..n} 1/(3*k-2)!!!.

%F a(n) = (3*n-2) * a(n-1) + 1.

%o (PARI) a007559(n) = prod(k=1, n, 3*k-2);

%o a(n) = a007559(n)*sum(k=0, n, 1/a007559(k));

%Y Row sums of A136214.

%Y Cf. A007559, A112293, A368791.

%K nonn,easy

%O 0,2

%A _Seiichi Manyama_, Jan 05 2024