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A078587
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Largest prime p such that p<n and 2n-p is also prime.
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6
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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, 29, 19, 23, 29, 31, 29, 31, 31, 29, 37, 37, 29, 41, 19, 41, 43, 31, 41, 43, 37, 47, 43, 43, 47, 47, 43, 53, 53, 43, 47, 59, 43, 53, 59, 61, 59, 61, 61, 53, 67, 67, 59, 71, 67, 59, 71
(list; graph; refs; listen; history; internal format)
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OFFSET
| 4,1
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COMMENTS
| Suggested by Goldbach Conjecture.
Also, values of p from A143697. This follows from the factorization n^2-k^2 = (n-k)(n+k). - T. D. Noe (noe(AT)sspectra.com), Jan 22 2009
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LINKS
| P. CAMI, Table of n, a(n) for n = 4..60000
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FORMULA
| a(n) = 2n - A078496(n)
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MATHEMATICA
| Table[p=n+1; q=2n-p; While[q>0&&!(PrimeQ[p]&&PrimeQ[q]), p++; q-- ]; q, {n, 4, 100}]
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CROSSREFS
| Cf. A143697, A078496.
Cf. A082467
Sequence in context: A131919 A204022 A131832 * A033558 A046217 A057662
Adjacent sequences: A078584 A078585 A078586 * A078588 A078589 A078590
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KEYWORD
| easy,nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Dec 02 2002
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Jan 24 2009 at the suggestion of R. J. Mathar and T. D. Noe.
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