|
| |
|
|
A094550
|
|
Numbers n such that there are integers a < b with a+(a+1)+...+(n-1) = (n+1)+(n+2)+...+b.
|
|
6
| |
|
|
4, 6, 9, 11, 14, 15, 16, 17, 19, 21, 22, 23, 24, 25, 26, 29, 30, 31, 32, 34, 35, 36, 38, 39, 40, 41, 43, 44, 46, 48, 49, 50, 51, 52, 53, 54, 56, 57, 59, 61, 64, 66, 68, 69, 70, 71, 72, 74, 76, 77, 79, 81, 82, 83, 84, 86, 87, 89, 91, 93, 94, 95, 96, 97, 98, 99, 100, 101, 104
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| Liljestrom shows that n is in this sequence if and only if 4n^2+1 is composite. Complement of A001912.
|
|
|
LINKS
| R. J. Liljestrom and Richard Zucker, Numerical Fulcrums (PowerPoint Format)
|
|
|
EXAMPLE
| 6 is in this sequence because 1+2+3+4+5 = 7+8.
|
|
|
MATHEMATICA
| lst={}; Do[i1=n-1; i2=n+1; s1=i1; s2=i2; While[i1>1 && s1!=s2, If[s1<s2, i1--; s1=s1+i1, i2++; s2=s2+i2]]; If[s1==s2, AppendTo[lst, n]], {n, 2, 140}]; lst
lst={}; Do[p=n^2+1; If[PrimeQ[p], AppendTo[lst, n/2]], {n, 2, 6!}]; lst; Complement[Range[358], lst] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Apr 09 2010]
Select[Range[1000], !PrimeQ[4#^2+1]&] [From T. D. Noe (noe(AT)sspectra.com), Nov 12 2010]
|
|
|
CROSSREFS
| Cf. A094551, A094552, A094553.
Sequence in context: A184814 A190001 A189532 * A122183 A189756 A133578
Adjacent sequences: A094547 A094548 A094549 * A094551 A094552 A094553
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| T. D. Noe (noe(AT)sspectra.com), May 10 2004
|
| |
|
|
