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A329470
a(n) = 2 a(n-1)^2 + 1 for n >=2 , where a(0) = 1, a(1) = 1.
0
1, 1, 3, 19, 723, 1045459, 2185969041363, 9556921299594946409795539, 182669489453303118864862198078197846848343568601043, 66736284754260838751569986258667504511444731209422184665239731909577328659648804587017101288201375699
OFFSET
0,3
COMMENTS
(a(n)) is a strong divisibility sequence.
FORMULA
a(n) = p(n,0), where p(n,x) is polynomial defined in A329432.
MATHEMATICA
f[x_] := 2 x^2 + 1; u[0, x_] := 1;
u[1, x_] := f[x]; u[n_, x_] := f[u[n - 1, x]]
Table [u[n, x] /. x -> 0, {n, 0, 10}]
CROSSREFS
Cf. A329432.
Sequence in context: A136372 A272571 A355615 * A107706 A373626 A330040
KEYWORD
nonn
AUTHOR
Clark Kimberling, Dec 31 2019
STATUS
approved