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A121852
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Numbers n such that partial sum of Catalan numbers A014137(n) is a prime.
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2
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1, 4, 6, 16, 24, 104, 121, 283, 326, 489, 1387, 1394, 1424, 1435, 1985, 4323, 5221
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Corresponding primes are A014137( a(n)) = {2,23,197,48760367,1757900019101,...}.
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EXAMPLE
| Catalan numbers A000108(n) begin {1,1,2,5,14,42,132,429,1430,4862,...}.
a(1) = 1 because A014137(1) = 1 + 1 = 2 is prime,
a(2) = 4 because A014137(4) = 1 + 1 + 2 + 5 + 14 = 23 is prime.
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MATHEMATICA
| s = 1; Do[s = s + (2n)!/((n!)^2(n + 1)); If[PrimeQ@s, Print@n], {n, 17925}] (* Robert G. Wilson v *)
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CROSSREFS
| Cf. A000108, A014137.
Sequence in context: A120375 A025618 A133572 * A122537 A059736 A102731
Adjacent sequences: A121849 A121850 A121851 * A121853 A121854 A121855
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KEYWORD
| hard,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Aug 30 2006
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EXTENSIONS
| a(11) - a(17) from Robert G. Wilson v, Aug 31 2006
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