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%I #19 Jan 01 2024 02:02:54
%S 3,3,5,3,5,7,7,5,11,7,11,13,13,11,17,7,17,19,13,17,19,19,23,23,19,17,
%T 29,19,23,29,31,29,31,31,29,37,37,29,41,19,41,43,31,41,43,37,47,43,43,
%U 47,47,43,53,53,43,47,59,43,53,59,61,59,61,61,53,67,67,59,71,67,59,71
%N Largest prime p such that p<n and 2n-p is also prime.
%C Suggested by Goldbach Conjecture.
%C Also, values of p from A143697. This follows from the factorization n^2-k^2 = (n-k)(n+k). - _T. D. Noe_, Jan 22 2009
%H P. CAMI, <a href="/A078587/b078587.txt">Table of n, a(n) for n = 4..60000</a>
%F a(n) = 2n - A078496(n)
%t Table[p=n+1; q=2n-p; While[q>0&&!(PrimeQ[p]&&PrimeQ[q]), p++; q-- ]; q, {n, 4, 100}]
%o (PARI) a(n) = {my(p = precprime(n-1)); while(!isprime(2*n-p), p = precprime(p-1)); p;} \\ _Michel Marcus_, Oct 22 2016
%Y Cf. A143697, A078496.
%Y Cf. A082467.
%K easy,nonn
%O 4,1
%A _T. D. Noe_, Dec 02 2002
%E Edited by _N. J. A. Sloane_, Jan 24 2009 at the suggestion of _R. J. Mathar_ and _T. D. Noe_.
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