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A084307
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a(n)=x is the least number such that GCD[sigma(x), sigma(x+1)]=n.
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1
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1, 13, 17, 6, 199, 5, 242, 27, 391, 57, 1296, 22, 882, 12, 648, 93, 175232, 89, 3872, 236, 195, 1032, 4875263, 14, 5739271, 467, 35377, 83, 1882384, 58, 3024, 308, 29240, 201, 1627208, 118, 79524, 147, 1682, 56
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| n=9: GCD[sigma[x+1], sigma[x]]=5 holds for {391,799,800,881,...} of which the first is a(9)=391.
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MATHEMATICA
| f[x_] := GCD[DivisorSigma[1, x], DivisorSigma[1, x+1]] t=Table[0, {256}]; Do[s=f[n]; If[s<257&&t[[s]]==0, t[[s]]=n], {n, 1, 10000000}]; t
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CROSSREFS
| Cf. A000203, A065444, A060780.
Sequence in context: A029526 A173632 A061060 * A066918 A164062 A117326
Adjacent sequences: A084304 A084305 A084306 * A084308 A084309 A084310
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jun 13 2003
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