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A068196
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Origin numbers: integers unreachable by Bergerson's Alpha construction (see the Ross Eckler link).
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1
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28, 108, 6902, 16068, 30662, 84662, 117157, 175844, 305804, 636268, 760436, 765402, 1343537, 1433493, 2125253, 3125825, 3255917, 4264947, 4796654, 10271188, 11911557, 12043892, 15344303, 27692262, 28112662, 28478708
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OFFSET
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1,1
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COMMENTS
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Note that Bergerson's Alpha construction is applied to composite numbers only. Otherwise the sequence could not contain numbers which are twice a prime, like 30662 and 84662. - Giovanni Resta, Mar 11 2013
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REFERENCES
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R. K. Guy, Unsolved Problems in Number Theory, F31. Japanese edition, 1983. [The English edition is different.]
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LINKS
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EXAMPLE
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The number 87 is not in the sequence because it can be reached from 90 = 2*3*3*5, since 87 = 90-2-3-3+5. - Giovanni Resta, Mar 11 2013
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MATHEMATICA
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seq[n_] := Block[{T = 0*Range@n, f, m}, m[{p_, e_}] := p*Range[-e, e, 2]; Do[f = FactorInteger@z; If[Last/@f != {1}, T[[Select[z + Union[ Total /@ Tuples[m /@ f]], 0 < # <= n &]]] = 1], {z, 4, 2*n+4}]; Flatten@Position[T, 0]]; seq[10^5] (* Giovanni Resta, Mar 11 2013 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Edited with three more terms based on the Ross Eckler article by Omar E. Pol, Sep 11 2010
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STATUS
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approved
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