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 A019470 #34 Dec 25 2022 02:16:42 %S A019470 1,5,7,10,11,13,14,17,18,19,20,21,22,23,24,25,26,28,29,31,34,35,37,38, %T A019470 40,41,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63, %U A019470 65,66,67,68,69,70,71,72,73,74,75,76,77,78,79 %N A019470 Numbers k that divide binomial(2*k-4, k-2). %C A019470 Old name was: (n-2)-nd Catalan number is divisible by n. %C A019470 For k in this sequence, convex k-gons have a number of triangulations that is divisible by k. - _David Eppstein_, Dec 24 2022 %H A019470 Charles R Greathouse IV, <a href="/A019470/b019470.txt">Table of n, a(n) for n = 1..10000</a> %p A019470 A019470:=n->`if`(binomial(2*n-4,n-2) mod n = 0,n,NULL): seq(A019470(n), n=1..70); # _Wesley Ivan Hurt_, Sep 13 2014 %t A019470 Select[Range[100],Divisible[Binomial[2#-4,#-2],#]&] (* _Giorgos Kalogeropoulos_, Aug 20 2021 *) %o A019470 (PARI) valp(n,p)=my(s); while(n\=p, s+=n); s %o A019470 bin(n,p)=valp(2*n,p)-2*valp(n,p) %o A019470 is(n)=my(f=factor(n)); for(i=1,#f~, if(bin(n-2,f[i,1])<f[i,2], return(0))); 1 \\ _Charles R Greathouse IV_, Nov 04 2016 %Y A019470 Complement of A019469. Cf. A000108. %K A019470 nonn %O A019470 1,2 %A A019470 _Wouter Meeussen_ %E A019470 More terms from _Wesley Ivan Hurt_, Sep 13 2014 %E A019470 Offset corrected by _Robert Israel_, Sep 14 2014 %E A019470 Name changed by _Wesley Ivan Hurt_, Sep 16 2014