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A290985
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Number of amicable pairs with lesser member at most 2^n.
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1
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0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 3, 5, 7, 8, 9, 16, 22, 30, 42, 57, 68, 95, 133, 167, 205, 257, 342, 460, 605, 786, 1043, 1356, 1749, 2294, 2905, 3757, 4811, 6181, 7893, 10146, 13051, 16762, 21396, 27380, 34939, 44449, 56481, 71453, 90783, 115200, 145702, 184045, 232899, 294326, 372216
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OFFSET
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1,11
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COMMENTS
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Sergei Chernykh led a BOINC project to find a(64) = 2390655. The project took 7 months and used several hundred CPU-years of computation time.
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LINKS
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PROG
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(PARI) has(n, f=factor(n))=my(t=sigma(f)-n); t>n && sigma(t)==n+t
a(n)=my(s); forfactored(k=1, 2^n, if(has(k[1], k[2]), s++)); s
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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STATUS
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approved
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