A015729 - OEIS

A015729

Numbers n such that phi(n) * sigma(n) + 16 is a perfect square.

7, 21, 32, 46, 60, 77, 123, 124, 132, 221, 224, 254, 261, 287, 308, 312, 376, 437, 445, 506, 534, 539, 665, 680, 717, 752, 770, 798, 860, 948, 1239, 1264, 1340, 1517, 1519, 1617, 1628, 1815, 2021, 2275, 2288, 2320, 2379, 2400, 2871, 2890

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

OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..500

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

MATHEMATICA

Select[Range[3000], IntegerQ[Sqrt[EulerPhi[#]DivisorSigma[1, #]+16]]&] (* Harvey P. Dale, Dec 07 2012 *)

PROG

(Magma) [n: n in [1..3000] | IsSquare(EulerPhi(n) * SumOfDivisors(n)+16)]; // Vincenzo Librandi, Mar 14 2014

CROSSREFS

Sequence in context: A325553 A032639 A264619 * A271972 A001485 A230210

Adjacent sequences: A015726 A015727 A015728 * A015730 A015731 A015732

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

STATUS

approved