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 A242897 #14 Dec 13 2022 17:59:59 %S A242897 14,42,132,4862,35357670,1767263190,91482563640,4861946401452, %T A242897 212336130412243110,2622127042276492108820,10113918591637898134020, %U A242897 39044429911904443959240,116157871455782434250553845880,6852456927844873497549658464312,368479169875816659479009042713546950 %N A242897 Catalan numbers C(n) such that sum of the factorials of digits of C(n) is semiprime. %C A242897 The n-th Catalan number is C(n) = (2*n)!/(n!*(n+1)!). %C A242897 a(347), having 998 digits, is the last term in b-file. %C A242897 a(348) has 1003 digits, hence is not included in b-file. %C A242897 Intersection of A000108 and A242868. %H A242897 K. D. Bajpai, <a href="/A242897/b242897.txt">Table of n, a(n) for n = 1..347</a> %e A242897 a(2) = 42 = (2*5)!/(5!*(5+1)!) is 5th Catalan number: 4!+2! = 26 = 2 * 13 which is semiprime. %e A242897 a(4) = 4862 = (2*9)!/(9!*(9+1)!) is 9th Catalan number: 4!+8!+6!+2! = 41066 = 2 * 20533 which is semiprime. %p A242897 with(numtheory): A242897:= proc() if bigomega(add( i!,i = convert(((2*n)!/(n!*(n+1)!)), base, 10))((2*n)!/(n!*(n+1)!)))=2 then RETURN ((2*n)!/(n!*(n+1)!)); fi; end: seq(A242897 (), n=1..100); %t A242897 Select[CatalanNumber[Range[70]],PrimeOmega[Total[IntegerDigits[#]!]]==2&] (* _Harvey P. Dale_, Dec 13 2022 *) %Y A242897 Cf. A000108, A001358, A061602, A242855, A242868. %K A242897 nonn,base,less %O A242897 1,1 %A A242897 _K. D. Bajpai_, May 25 2014