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Search: id:A094550
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| A094550 |
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Numbers n such that there are integers a < b with a+(a+1)+...+(n-1) = (n+1)+(n+2)+...+b. |
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+0
7
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| 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; listen)
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OFFSET
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1,1
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COMMENT
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Liljestrom shows that n is in this sequence if and only if 4n^2+1 is composite. Complement of A001912.
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LINKS
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R. J. Liljestrom and Richard Zucker, Numerical Fulcrums (PowerPoint Format)
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EXAMPLE
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6 is in this sequence because 1+2+3+4+5 = 7+8.
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MATHEMATICA
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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
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CROSSREFS
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Cf. A094551, A094552, A094553.
Sequence in context: A085842 A131220 A060106 this_sequence A122183 A133578 A010387
Adjacent sequences: A094547 A094548 A094549 this_sequence A094551 A094552 A094553
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), May 10 2004
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