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A134020
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Numbers that are one less than a square and have exactly 4 divisors.
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1
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8, 15, 35, 143, 323, 899, 1763, 3599, 5183, 10403, 11663, 19043, 22499, 32399, 36863, 39203, 51983, 57599, 72899, 79523, 97343, 121103, 176399, 186623, 213443, 272483, 324899, 359999, 381923, 412163, 435599, 656099, 675683, 685583, 736163
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OFFSET
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1,1
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COMMENTS
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LINKS
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MAPLE
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with(numtheory): a:=proc(n) if type(sqrt(n+1), integer)=true and tau(n)=4 then n else end if end proc: seq(a(n), n=1..800000); # Emeric Deutsch, Jan 27 2008
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MATHEMATICA
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t={}; Do[If[DivisorSigma[0, n]==4&&IntegerQ[Sqrt[n+1]], AppendTo[t, n]], {n, 10^6}]; t (* Jayanta Basu, Jun 03 2013 *)
Select[Range[1000]^2-1, DivisorSigma[0, #]==4&] (* Harvey P. Dale, Jul 28 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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