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A090259 Least even a(n) > 2 not representable as a sum of two of the first n primes. From Goldbach conjecture. 1
6, 8, 12, 16, 20, 28, 32, 40, 44, 44, 56, 64, 76, 76, 92, 92, 92, 110, 116, 116, 136, 136, 148, 164, 174, 182, 188, 188, 220, 224, 232, 242, 242, 256, 260, 272, 272, 292, 292, 292, 332, 350, 350, 368, 368, 368, 400, 400, 412, 412, 436, 442, 442, 476, 476, 476 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n)<=2p(n)+2, where p(n) is the n-th prime.

The only even prime number, 2, is not able to be represented as a sum of two primes. - Lei Zhou, Apr 09 2014

LINKS

Lei Zhou, Table of n, a(n) for n = 1..10000

EXAMPLE

a(5)=20 since {2,3,5,7,11} can't represent 20 as a sum of two primes.

MATHEMATICA

a = {}; c = 6; Table[p = Prime[n]; Do[q = Prime[k]; If[sum = p + q; ! MemberQ[a, sum], AppendTo[a, sum]], {k, PrimePi[NextPrime[c - p, -1]], n}]; While[MemberQ[a, c], c = c + 2]; c, {n, 1, 100}] (*Lei Zhou, Apr 09 2014*)

CROSSREFS

Cf. A002372.

Sequence in context: A194409 A115166 A050992 * A089241 A280270 A315862

Adjacent sequences:  A090256 A090257 A090258 * A090260 A090261 A090262

KEYWORD

nonn

AUTHOR

Ed T. Prothro (prothro(AT)compuserve.com), Jan 24 2004

EXTENSIONS

Flaw in the title fixed by Lei Zhou, Apr 09 2014

STATUS

approved

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Last modified November 24 04:08 EST 2020. Contains 338607 sequences. (Running on oeis4.)