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Numbers n such that partial sum of Catalan numbers A014137(n) is a prime.
2

%I #6 Mar 20 2015 18:26:56

%S 1,4,6,16,24,104,121,283,326,489,1387,1394,1424,1435,1985,4323,5221

%N Numbers n such that partial sum of Catalan numbers A014137(n) is a prime.

%C Corresponding primes are A014137( a(n)) = {2,23,197,48760367,1757900019101,...}.

%e Catalan numbers A000108(n) begin {1,1,2,5,14,42,132,429,1430,4862,...}.

%e a(1) = 1 because A014137(1) = 1 + 1 = 2 is prime,

%e a(2) = 4 because A014137(4) = 1 + 1 + 2 + 5 + 14 = 23 is prime.

%t s = 1; Do[s = s + (2n)!/((n!)^2(n + 1)); If[PrimeQ@s, Print@n], {n, 17925}] (* _Robert G. Wilson v_ *)

%Y Cf. A000108, A014137.

%K hard,nonn

%O 1,2

%A _Alexander Adamchuk_, Aug 30 2006

%E a(11) - a(17) from _Robert G. Wilson v_, Aug 31 2006