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Search: id:A134989
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| A134989 |
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Numbers expressible in more than one way as 6^x-y^2. |
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+0
2
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| 0, 20, 32, 95, 207, 720, 1152, 1215, 1287, 3420, 3807, 6255, 6407, 7452, 7767, 18095, 23247, 25920, 41472, 43740, 46332, 46647, 69255, 123120, 137052, 174087, 211815, 217935, 225180, 230652, 268272, 279612, 279927, 651420, 836892, 933120, 1416447
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers n such that equation 6^x-y^2=n has more than one solution.
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EXAMPLE
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0=6^(2k)-(6^k)^2, k=1,2,..
20=6^2-4^2=6^3-14^2,
32=6^2-2^2=6^5-88^2,
95=6^3-11^2=6^7-529^2,
207=6^3-3^2=6^4-33^2=6^5-87^2,
720=6^4-24^2=6^5-84^2,
1152=6^4-12^2=6^7-528^2,
1215=6^4-9^2=6^5-81^2,
1287=6^4-3^2=6^6-213^2.
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MATHEMATICA
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lst = {}; Do[ t = 6^x - y^2; If[t < 10^7/7, AppendTo[lst, t]], {x, 185}, {y, (a = Floor@Sqrt[6^x - 10^7]; If[Element[a, Reals], a, 0]), Floor@Sqrt[6^x]}]; lst = Sort@lst; lsu = {}; Do[ If[lst[[n]] == lst[[n + 1]], AppendTo[lsu, lst[[n]]]], {n, -1 + Length@lst}]; Union@lsu - Robert G. Wilson v (rgwv(AT)rgwv.com), Feb 09 2008
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CROSSREFS
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Cf. A051217.
Sequence in context: A075035 A032352 A124665 this_sequence A119873 A075230 A165236
Adjacent sequences: A134986 A134987 A134988 this_sequence A134990 A134991 A134992
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Feb 05 2008
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Feb 09 2008
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