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A137826
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Least prime number that produces the highest abundancy number when multiplied by the product of all previous n-1 terms.
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2
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2, 3, 5, 2, 7, 11, 3, 13, 2, 17, 19, 23, 29, 2, 5, 31, 37, 3, 41, 43, 47, 53, 7, 59, 61, 2, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 3, 2, 127, 131, 11, 137, 139, 149, 151, 5, 157, 163, 167, 173, 179, 181, 13, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241
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OFFSET
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1,1
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COMMENTS
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"Least" is required in the definition, otherwise a(14) could be either 2 or 5 because 2*77636318760 and 5*77636318760 have the same abundancy. It appears that only a(14) has this property. - T. D. Noe, Jan 24 2010
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LINKS
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Eric Weisstein's World of Mathematics, Abundancy.
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EXAMPLE
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a(4)=2 since the product a(1)*a(2)*a(3) is 2*3*5=30, and
30*2 = 60 has abundancy 2.8, whereas
30*3 = 90 has abundancy 2.6,
30*5 = 150 has abundancy 2.48,
30*7 = 210 has abundancy 2.7428571..., etc.
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MATHEMATICA
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Abundancy[k_Integer] := DivisorSigma[1, k]/k; SetAttributes[Abundancy, Listable]; nn=100; lastPrime=1; n=1; Table[a=Abundancy[n*Prime[Range[lastPrime+1]]]; pos=Position[a, Max[a]]; p=Prime[pos[[1, 1]]]; If[pos[[1, 1]>lastPrime, lastPrime++ ]; n=n*p; p, {nn}] (* T. D. Noe, Jan 24 2010 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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