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A247473
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Numbers of the form 2^k (k>=0) that are a sum of divisors of n for some n.
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0
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1, 4, 8, 32, 128, 256, 512, 1024, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648, 4294967296, 8589934592, 17179869184, 34359738368
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OFFSET
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1,2
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COMMENTS
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Corresponding values of numbers k>0 are in A180221.
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LINKS
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FORMULA
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a(1) = 1, for n>=2, a(n) = 2^A180221(n-1).
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EXAMPLE
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32 = 2^5 is in sequence because there are numbers n = 21 and 31 with sigma(n) = 32.
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PROG
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(Magma) Set(Sort([SumOfDivisors(n): n in [A046528(n)]]))
(Magma) Set(Sort([SumOfDivisors(n): n in[1..10000], k in [0..100] | SumOfDivisors(n) eq 2^k]))
(Magma) [1] cat [2^n: n in[A180221(n)]]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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