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 A128287 #18 May 08 2025 19:41:20
%S A128287 1,8,133,49378
%N A128287 Nonprime numbers k such that k divides A014137(k).
%C A128287 Prime p divides A014137(p) for p in A045309 (primes congruent to {0, 2} mod 3).
%C A128287 a(5) > 5000000. - _Chai Wah Wu_, Nov 13 2014
%e A128287 1 is nonprime and divides A014137(1) = 2, so 1 is a term.
%e A128287 8 is nonprime and divides A014137(8) = 2056, so 8 is a term.
%t A128287 s = 1; Do[s = s + (2n)!/n!/(n+1)!; If[ !PrimeQ[n] && Mod[s, n] == 0, Print[n]], {n, 1000}]
%o A128287 (Python)
%o A128287 from __future__ import division
%o A128287 from sympy import isprime
%o A128287 A128287_list, x, s = [1], 1, 2
%o A128287 for i in range(2,10**5):
%o A128287 x = x*(4*i-2)//(i+1)
%o A128287 s += x
%o A128287 if not (isprime(i) or s % i):
%o A128287 A128287_list.append(i) # _Chai Wah Wu_, Nov 13 2014
%Y A128287 Cf. A014137, A000108, A045309, A045309.
%K A128287 bref,hard,more,nonn
%O A128287 1,2
%A A128287 _Alexander Adamchuk_, Feb 23 2007
%E A128287 One more term from _Ryan Propper_, Apr 02 2007