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 A053427 #20 Apr 26 2021 11:33:53
%S A053427 4,5,6,8,9,18,25,66,87,134,145,200,384,443,502,589,625,638,1082,1235,
%T A053427 1236,1439,1892,2014,2355,2380,2592,2676,2981,3406,3908,4775,5885,
%U A053427 10617,16108,17035,18164,18307,20565,24542,26388,32786,47379,49711,50103,55067
%N A053427 Numbers n such that Catalan(n)-1 is prime.
%C A053427 Primality up to Catalan(5885)-1 proved by PrimeForm.
%C A053427 The next term, if it exists, is > 60000. - _Vaclav Kotesovec_, Apr 26 2021
%e A053427 Catalan(25)-1 = 50!/25!/26!-1 = 4861946401451 is prime.
%t A053427 Reap[ Do[ If[ PrimeQ[ CatalanNumber[n] - 1], Print[n]; Sow[n]], {n, 0, 10^4}]][[2, 1]] (* _Jean-François Alcover_, Feb 02 2015 *)
%o A053427 (PARI) is(n)=ispseudoprime(binomial(2*n,n)/(n+1)-1) \\ _Charles R Greathouse IV_, Jan 03 2014
%o A053427 (PFGW) ABC2 C(2*$a,$a)/($a+1)-1
%o A053427 a: from 5886 to 100000
%o A053427 _Charles R Greathouse IV_, Jan 03 2014
%Y A053427 Cf. A000108, A053429.
%K A053427 nonn
%O A053427 1,1
%A A053427 _David Broadhurst_, Jan 10 2000
%E A053427 a(34)-a(41) from _Charles R Greathouse IV_, Jan 03 2014
%E A053427 a(42) from _Vaclav Kotesovec_, Apr 20 2021
%E A053427 a(43)-a(46) from _Vaclav Kotesovec_, Apr 25 2021