A090259 Least even a(n) > 2 not representable as a sum of two of the first n primes. From Goldbach conjecture.

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

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 A368242

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