A368790 a(n) = (3*n-2)!!! * Sum_{k=0..n} 1/(3*k-2)!!!.
1, 2, 9, 64, 641, 8334, 133345, 2533556, 55738233, 1393455826, 39016763129, 1209519657000, 41123668338001, 1521575728506038, 60863029140241521, 2617110253030385404, 120387071639397728585, 5898966510330488700666, 306746258537185412434633
Offset: 0
Programs
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PARI
a007559(n) = prod(k=1, n, 3*k-2); a(n) = a007559(n)*sum(k=0, n, 1/a007559(k));
Formula
a(n) = (3*n-2) * a(n-1) + 1.