OFFSET
1,1
COMMENTS
The n-th Catalan number Catalan(n) = (2*n)!/(n!*(n+1)!).
The 40th term in the sequence, a(40), has 651 digits.
a(41), a(42), and a(43), which are not included in the b-file, have 1313, 1313, and 1317 digits, respectively.
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..40
EXAMPLE
16796 is in sequence because Catalan(10) = (2*10)!/(10!*(10+1)!) = 16796: The digital sum(16796) = 29 which is prime.
208012 is in sequence because Catalan(12) = (2*12)!/(12!*(12+1)!) = 208012: The digital sum(208012) = 13 which is prime.
MAPLE
KD := proc() local a, b; a:=(2*n)!/(n!*(n+1)!); b:=add( i, i = convert((a), base, 10))(a); if isprime(b) then RETURN (a); fi; end: seq(KD(), n=1..200);
MATHEMATICA
Select[CatalanNumber[Range[100]], PrimeQ[Total[IntegerDigits[#]]]&] (* Harvey P. Dale, Jul 19 2019 *)
CROSSREFS
KEYWORD
nonn,less,base
AUTHOR
K. D. Bajpai, Apr 05 2014
STATUS
approved