The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A015728 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A015728

Numbers n such that phi(n) * sigma(n) + 9 is a perfect square.
(history; published version)

#16 by Charles R Greathouse IV at Thu Sep 08 08:44:40 EDT 2022

PROG

(MAGMAMagma) [n: n in [1..6000] | IsSquare(EulerPhi(n) * SumOfDivisors(n) + 9)]; // Vincenzo Librandi, Mar 14 2014

Discussion

Thu Sep 08

08:44

OEIS Server: https://oeis.org/edit/global/2944

#15 by Michel Marcus at Fri Mar 14 06:30:20 EDT 2014

STATUS

reviewed

approved

#14 by Joerg Arndt at Fri Mar 14 05:51:27 EDT 2014

STATUS

proposed

reviewed

#13 by Michel Marcus at Fri Mar 14 05:41:39 EDT 2014

STATUS

editing

proposed

#12 by Michel Marcus at Fri Mar 14 05:41:25 EDT 2014

REFERENCES

R. K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.

LINKS

Richard K. Guy, <a href="http://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360.

STATUS

proposed

editing

#11 by Vincenzo Librandi at Fri Mar 14 03:29:42 EDT 2014

STATUS

editing

proposed

#10 by Vincenzo Librandi at Fri Mar 14 03:29:34 EDT 2014

PROG

(MAGMA) [n: n in [1..6000] | IsSquare(EulerPhi(n) * SumOfDivisors(n) + 9)]; // Vincenzo Librandi, Mar 14 2014

STATUS

proposed

editing

#9 by Vincenzo Librandi at Fri Mar 14 02:59:22 EDT 2014

STATUS

editing

proposed

#8 by Vincenzo Librandi at Fri Mar 14 02:59:08 EDT 2014

LINKS

Vincenzo Librandi, <a href="/A015728/b015728.txt">Table of n, a(n) for n = 1..210</a>

MATHEMATICA

Select[Range[10000], IntegerQ[Sqrt[EulerPhi[#]DivisorSigma[1, #] + 9]] &] (* Vincenzo Librandi, Mar 14 2014 *)

STATUS

approved

editing

#7 by Russ Cox at Fri Mar 30 17:30:16 EDT 2012

AUTHOR

_Robert G. Wilson v (rgwv(AT)rgwv.com)_

Discussion

Fri Mar 30

17:30

OEIS Server: https://oeis.org/edit/global/156