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%I #7 Jun 18 2021 12:17:32
%S 511,537,999,1073,1239,1461,1501,1541,1763,1773,1899,1917,2071,2181,
%T 2401,2409,2449,3059,3069,3179,3201,3509,3807,4081,4101,4179,4387,
%U 4399,4437,4467,4559,4607,4681,4705,4879,5089,5211,5257,5271,5373,5429,5757,5829,6415,6621,6671
%N Composite numbers that are the exact average of three consecutive primes.
%e 511 is composite and the average of the consecutive primes 503, 509 and 521. Thus, 511 is in the sequence.
%t Select[Table[(Prime[n] + Prime[n + 1] + Prime[n + 2])/3, {n, 2000}], IntegerQ[#] && ! PrimeQ[#] &]
%Y Cf. A242218 (subsequence of semiprimes).
%K nonn
%O 1,1
%A _Tanya Khovanova_, Jun 16 2021