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 A345363 #12 Feb 01 2025 17:11:47
%S A345363 511,537,999,1073,1239,1461,1501,1541,1763,1773,1899,1917,2071,2181,
%T A345363 2401,2409,2449,3059,3069,3179,3201,3509,3807,4081,4101,4179,4387,
%U A345363 4399,4437,4467,4559,4607,4681,4705,4879,5089,5211,5257,5271,5373,5429,5757,5829,6415,6621,6671
%N A345363 Composite numbers that are the exact average of three consecutive primes.
%H A345363 Harvey P. Dale, <a href="/A345363/b345363.txt">Table of n, a(n) for n = 1..5000</a>
%e A345363 511 is composite and the average of the consecutive primes 503, 509 and 521. Thus, 511 is in the sequence.
%t A345363 Select[Table[(Prime[n] + Prime[n + 1] + Prime[n + 2])/3, {n, 2000}], IntegerQ[#] && ! PrimeQ[#] &]
%t A345363 Select[Mean/@Partition[Prime[Range[1000]],3,1],IntegerQ[#]&&CompositeQ[#]&] (* _Harvey P. Dale_, Feb 01 2025 *)
%Y A345363 Cf. A242218 (subsequence of semiprimes).
%K A345363 nonn
%O A345363 1,1
%A A345363 _Tanya Khovanova_, Jun 16 2021