%N Numbers k such that 2k + p is composite for all primes p, q with p + q = 2k.
%C Or, numbers k such that there is no prime p < 2k with 2k - p and 2k + p both prime.
%C The two initial terms vacuously satisfy the definition, but all even numbers >= 4 are the sum of two primes, according to the Goldbach conjecture.
%C See also A284919, twice this sequence, which lists the values of 2k.
%H Claudio Meller and others, <a href="http://list.seqfan.eu/pipermail/seqfan/2017-April/017433.html">New sequence</a>, SeqFan list, April 5, 2017. (Click "next" for subsequent contributions.)
%o (PARI) is_A284928(n)=!forprime(p=2,n, isprime(2*n-p) && (isprime(2*n+p) || isprime(4*n-p)) && return) \\ _M. F. Hasler_, Apr 06 2017
%Y Cf. A284919 (twice this), A002375 (number of decompositions p + q = 2k), A020481 (least p: p + q = 2k).
%A _M. F. Hasler_, Apr 06 2017