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A304276
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Numbers equal to the sum of their aliquot parts, each of them increased by 2.
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8
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OFFSET
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1,1
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COMMENTS
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Searched up to n = 10^12.
If p = 2^(1+t) + (1+2*t)*k - 1 is a prime, for some t > 0 and k even, then x = 2^t*p is in the sequence where k is the value by which the sum of aliquot parts is increased.
In this sequence k = 2; for t = 21 we get 8796271280128 which is a term greater than 2139136, but this does not exclude the existence of other intermediate terms following a different solution pattern.
(End)
Terms using odd values of k seem very hard to find. Up to n = 10^12, only three such terms are known: 2, 98, and 8450, for k = 1, 5, and -7, respectively.
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LINKS
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EXAMPLE
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Aliquot part of 3 is 1 and 1+2 = 3.
Aliquot parts of 15 are 1, 3, 5 and (1+2) + (3+2) + (5+2) = 15.
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MAPLE
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with(numtheory): P:=proc(q, k) local n;
for n from 1 to q do if 2*n=sigma(n)+k*(tau(n)-1) then print(n);
fi; od; end: P(10^12, 2);
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MATHEMATICA
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Select[Range[10^6], DivisorSum[#, # + 2 &] - (# + 2) == # &] (* Michael De Vlieger, May 14 2018 *)
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CROSSREFS
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Cf. A000005, A000203, A000396, A304277, A304278, A304279, A304280, A304281, A304282, A304283, A304284.
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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