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A060003 Odd numbers not of the form p + 2*k^2, k>0, p prime. 6
1, 3, 17, 137, 227, 977, 1187, 1493, 5777, 5993 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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 6n-1. - Dan Graham, Mar 03 2015

REFERENCES

David Wells, Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, Penguin Books, London, 1997, page 76.

LINKS

Table of n, a(n) for n=1..10.

Laurent Hodges, A lesser-known Goldbach conjecture, Math. Mag., 66 (1993), 45-47.

Mark VandeWettering, Toying with a lesser known Goldbach Conjecture

MATHEMATICA

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 } ]

PROG

(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

CROSSREFS

Cf. A042978.

Sequence in context: A105630 A199138 A006290 * A231909 A244432 A219503

Adjacent sequences:  A060000 A060001 A060002 * A060004 A060005 A060006

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Mar 14 2001

STATUS

approved

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Last modified December 10 23:13 EST 2016. Contains 279021 sequences.