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A085634
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Numbers of the form 2^a + 3^b = 2^c + 3^d for nonnegative a, b, c, d and a <> c.
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3
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(5) = 256 + 3 = 2^8 + 3^1 = 259 = 16 + 243 = 2^4 + 3^5.
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MATHEMATICA
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(* Max exponent 8 is sufficient to get all known solutions *)
f[_] = 0; Reap[Do[n = 2^a + 3^b; f[n] = f[n] + 1; If[f[n] == 1, ab[n] = {a, b}, If[f[n] >= 2, Print[HoldForm[2^x + 3^y] /. Thread[{x, y} -> ab[n]], " = ", HoldForm[2^x + 3^y] /. Thread[{x, y} -> {a, b}], " = ", n]; Sow[n]]], {a, 0, 8}, {b, 0, 8}]][[2, 1]] // Union (* Jean-François Alcover, Apr 29 2014 *)
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CROSSREFS
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KEYWORD
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nonn,fini,full
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AUTHOR
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STATUS
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approved
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