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A195382
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Numbers such that the difference between the sum of the even divisors and the sum of the odd divisors is prime.
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4
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4, 8, 16, 18, 32, 50, 256, 512, 578, 1458, 2048, 3362, 4802, 6962, 8192, 10082, 15842, 20402, 31250, 34322, 55778, 57122, 59858, 167042, 171698, 293378, 524288, 559682, 916658, 982802, 1062882, 1104098, 1158242, 1195058, 1367858, 1407842, 1414562
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OFFSET
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1,1
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COMMENTS
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Note that these are all even numbers. The odd numbers, producing the negative of a prime, are all squares whose square roots are in A193070. - T. D. Noe, Sep 19 2011
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LINKS
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Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
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EXAMPLE
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The divisors of 18 are { 1, 2, 3, 6, 9, 18}, and (2 + 6 + 18) - (1 + 3 + 9) = 13 is prime. Hence 18 is in the sequence.
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MAPLE
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with(numtheory):for n from 2 by 2 to 200 do:x:=divisors(n):n1:=nops(x):s1:=0:s2:=0:for m from 1 to n1 do:if irem(x[m], 2)=1 then s1:=s1+x[m]:else s2:=s2+x[m]:fi:od: if type(s2-s1, prime)=true then printf(`%d, `, n): else fi:od:
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MATHEMATICA
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f[n_] := Module[{d = Divisors[n], p}, p = Plus @@ Select[d, OddQ] - Plus @@ Select[d, EvenQ]; PrimeQ[p]]; Select[Range[2, 1000000, 2], f] (* T. D. Noe, Sep 19 2011 *)
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PROG
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(PARI) list(lim)=my(v=List(), t); forstep(n=3, sqrt(lim\2), 2, if(isprime(s=sigma(n^2)), listput(v, 2*n^2))); t=2; while((t*=2)<=lim, if(isprime(2*sigma(t/2)-1), listput(v, t))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Sep 18 2011
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CROSSREFS
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Subsequence of A088827.
Cf. A002129, A113184.
Sequence in context: A070738 A055744 A141718 * A211413 A181310 A212110
Adjacent sequences: A195379 A195380 A195381 * A195383 A195384 A195385
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KEYWORD
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nonn
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AUTHOR
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Michel Lagneau, Sep 17 2011
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STATUS
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approved
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