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 A134989 Numbers expressible in more than one way as 6^x-y^2. 1
 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; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that equation 6^x-y^2=n has more than one solution. LINKS EXAMPLE 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. MATHEMATICA 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, Feb 09 2008 CROSSREFS Cf. A051217. Sequence in context: A032352 A183048 A124665 * A119873 A075230 A165236 Adjacent sequences:  A134986 A134987 A134988 * A134990 A134991 A134992 KEYWORD nonn AUTHOR Zak Seidov, Feb 05 2008 EXTENSIONS More terms from Robert G. Wilson v, Feb 09 2008 STATUS approved

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Last modified October 19 15:49 EDT 2018. Contains 316365 sequences. (Running on oeis4.)