|
| |
|
|
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
|
|
|
|
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
|
|
|
|
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
|
| |
|
|
