A338816 a(0) = 1; for n > 0, a(n) = Sum_{k=0..n-1} prime(a(k)) * prime(a(n-k-1)).
1, 4, 28, 477, 15054, 716619, 46386636, 3829544473, 386956394842, 46498297487679, 6503866348955704, 1041432998153210277, 188367392877258840974
Offset: 0
Programs
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Mathematica
a[0] = 1; a[n_] := a[n] = Sum[Prime[a[k]] Prime[a[n - k - 1]], {k, 0, n - 1}]; Table[a[n], {n, 0, 9}]
Formula
G.f.: 1 + x * (Sum_{n>=0} prime(a(n)) * x^n)^2.
Extensions
a(10)-a(11) from Daniel Suteu, Nov 10 2020
a(12) from Jinyuan Wang, Nov 14 2020