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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..19.

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

Adjacent sequences:  A218481 A218482 A218483 * A218485 A218486 A218487

KEYWORD

nonn

AUTHOR

Jayanta Basu, Apr 11 2013

EXTENSIONS

a(16)-a(19) from Donovan Johnson, Apr 11 2013

STATUS

approved

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Last modified February 18 00:19 EST 2019. Contains 320237 sequences. (Running on oeis4.)