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A103289
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Numbers k such that both sigma(k) >= 2*k-1 and sigma(k+1) >= 2*(k+1)-1.
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4
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1, 4095, 5775, 5984, 7424, 11024, 21735, 21944, 26144, 27404, 39375, 43064, 49664, 56924, 58695, 61424, 69615, 70784, 76544, 77175, 79695, 81080, 81675, 82004, 84524, 84644, 89775, 91664, 98175, 103455, 104895, 106784, 109395, 111824
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OFFSET
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1,2
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COMMENTS
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Numbers k that both k and k+1 are in A103288.
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LINKS
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MAPLE
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with(numtheory): a:=`if`(sigma(n)>=2*n-1 and sigma(n+1)>=2*(n+1)-1, n, NULL): seq(a(n), n=1..120000); # Muniru A Asiru, Jun 26 2018
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MATHEMATICA
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Select[Range[120000], And[DivisorSigma[1, #] >= 2 #1 - 1, DivisorSigma[1, # + 1] >= 2 (#1 + 1) - 1] &] (* Michael De Vlieger, Jun 29 2018 *)
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PROG
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(PARI) for(i=1, 1000000, if(sigma(i)>=2*i-1 && sigma(i+1)>=2*i+1, print1(i, ", ")));
(GAP) Filtered([1..120000], n->Sigma(n)>=2*n-1 and Sigma(n+1)>2*(n+1)-1); # Muniru A Asiru, Jun 26 2018
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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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