This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A240435 #20 Jul 19 2019 12:32:17 %S A240435 2,5,14,16796,208012,18367353072152,14544636039226909, %T A240435 3116285494907301262,45950804324621742364,176733862787006701400, %U A240435 270557451039395118028642463289168566420671280440,3935312233584004685417853572763349509774031680023800 %N A240435 Catalan numbers whose sum of digits is a prime. %C A240435 The n-th Catalan number Catalan(n) = (2*n)!/(n!*(n+1)!). %C A240435 The 40th term in the sequence, a(40), has 651 digits. %C A240435 a(41), a(42), and a(43), which are not included in the b-file, have 1313, 1313, and 1317 digits, respectively. %H A240435 K. D. Bajpai, <a href="/A240435/b240435.txt">Table of n, a(n) for n = 1..40</a> %e A240435 16796 is in sequence because Catalan(10) = (2*10)!/(10!*(10+1)!) = 16796: The digital sum(16796) = 29 which is prime. %e A240435 208012 is in sequence because Catalan(12) = (2*12)!/(12!*(12+1)!) = 208012: The digital sum(208012) = 13 which is prime. %p A240435 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); %t A240435 Select[CatalanNumber[Range[100]],PrimeQ[Total[IntegerDigits[#]]]&] (* _Harvey P. Dale_, Jul 19 2019 *) %Y A240435 Cf. A000108, A230061, A231885. %K A240435 nonn,less,base %O A240435 1,1 %A A240435 _K. D. Bajpai_, Apr 05 2014