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A218484
Square numbers n for which sigma(n) - d(n) is also a perfect square.
0
1, 4, 1276900, 7236100, 9449476, 69529779225, 273137935876, 275693254225, 1011814692100, 1590221881600, 3007619594001, 5382738725329, 6343774129225, 10830009646404, 43037339281225, 49597341481444, 161977776248401, 492275260674729, 623724701219361
OFFSET
1,2
EXAMPLE
4 is in the list since 4 = 2^2 and sigma(4)-d(4) = 4 = 2^2. Also 9449476 = 3074^2 and sigma(9449476)-d(9449476) = 17455684 = 4178^2.
MATHEMATICA
Sqd[n_] := Sqrt[DivisorSigma[1, n] - DivisorSigma[0, n]]; t = {}; Do[p = n^2; If[IntegerQ[Sqd[p]], AppendTo[t, p]], {n, 7000000}]; t
CROSSREFS
Cf. A221856.
Sequence in context: A275685 A124119 A090096 * A046362 A144122 A058424
KEYWORD
nonn
AUTHOR
Jayanta Basu, Apr 11 2013
EXTENSIONS
a(16)-a(19) from Donovan Johnson, Apr 11 2013
STATUS
approved