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A060003
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Odd numbers not of the form p + 2*k^2, k>0, p prime.
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7
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OFFSET
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1,2
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COMMENTS
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This sequence is probably finite.
Goldbach conjectured that all odd composites are sum of a prime and twice a square. a(9) = 5777 and a(10) = 5993 are the only known exceptions. Elements a(2) .. a(8) are the odd Stern primes (cf. A042978). The next element of the sequence, if it exists, is larger than 10^9. - M. F. Hasler, Nov 16 2007
The next term, if it exists, is larger than 2 * 10^13. - Benjamin Chaffin, Mar 28 2008
Terms greater than 3 are of the form 6*n-1. - Dan Graham, Mar 03 2015
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REFERENCES
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David Wells, Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, Penguin Books, London, 1997, page 76.
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LINKS
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MATHEMATICA
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Do[ k = 1; While[ n - 2*k^2 > 1 && !PrimeQ[ n - 2*k^2 ], k++ ]; If[ n - 2*k^2 < 0, Print[n] ], { n, 5, 10^8 } ]
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PROG
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(PARI) forstep( n=1, 2^30, 2, for(s=1, sqrtint(n\2), if(isprime(n-2*s^2), next(2))); print(n)) \\ M. F. Hasler, Nov 16 2007
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CROSSREFS
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KEYWORD
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nonn,hard,more
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AUTHOR
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STATUS
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approved
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