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A126105
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Prime(n)^2*prime(n+1)...*prime(a(n)) is the least product of consecutive primes which is abundant. Note that only the first term is squared.
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1
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2, 5, 10, 20, 34, 50, 72, 97, 129, 165, 203, 248, 295, 346, 405, 469, 537, 607, 685, 766, 853, 949, 1049, 1155, 1264, 1376, 1494, 1620, 1754, 1897, 2048, 2193, 2346, 2503, 2669, 2836, 3012, 3193, 3378, 3572, 3770, 3973, 4186, 4400, 4624, 4855, 5098, 5339, 5578
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(3)=10 since x=5^2*7*11*13*17*19*23*29=5391411025 is abundant with sigma(x)=10799308800 and sigma(x)-2*x=16486750.
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MATHEMATICA
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a[n_] := Module[{p = Prime[n]}, c = 1; pr = 1 + 1/p + 1/p^2; While[pr < 2, p = NextPrime[p]; pr *= (1 + 1/p); c++]; c + n - 1]; Array[a, 50] (* Amiram Eldar, Aug 14 2019 *)
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CROSSREFS
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KEYWORD
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less,nonn
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AUTHOR
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EXTENSIONS
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a(21) corrected and more terms added by Amiram Eldar, Aug 14 2019
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STATUS
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approved
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