A218484 Square numbers n for which sigma(n) - d(n) is also a perfect square.

1, 4, 1276900, 7236100, 9449476, 69529779225, 273137935876, 275693254225, 1011814692100, 1590221881600, 3007619594001, 5382738725329, 6343774129225, 10830009646404, 43037339281225, 49597341481444, 161977776248401, 492275260674729, 623724701219361

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