The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 5 03:59 EST 2021. Contains 349530 sequences. (Running on oeis4.)