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A083540 A083539[n] is a square; solutions x to sigma[x+1].sigma[x]=y^2 for some y. 3
14, 30, 51, 161, 186, 206, 223, 329, 552, 713, 759, 869, 957, 994, 995, 1248, 1334, 1364, 1634, 1715, 1819, 2093, 2133, 2584, 2685, 2820, 2821, 2974, 3115, 3145, 3485, 4212, 4308, 4312, 4364, 4408, 4649 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

x=30: sigma[30]=72, sigma[31]=32,product=72.32=256.9=24^2

MATHEMATICA

Do[s=Sqrt[DivisorSigma[1, n+1]*DivisorSigma[1, n]]; If[IntegerQ[s], Print[n]], {n, 1, 5000}]

Flatten[Position[Times@@@Partition[DivisorSigma[1, Range[5000]], 2, 1], _?(IntegerQ[Sqrt[#]]&)]] (* Harvey P. Dale, Mar 07 2016 *)

CROSSREFS

Cf. A000203, A083539, A060780, A060781, A083538.

Sequence in context: A044456 A132759 A011257 * A027575 A104776 A308312

Adjacent sequences:  A083537 A083538 A083539 * A083541 A083542 A083543

KEYWORD

nonn

AUTHOR

Labos Elemer, May 21 2003

STATUS

approved

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Last modified December 15 09:05 EST 2019. Contains 329995 sequences. (Running on oeis4.)