A015728 Numbers n such that phi(n) * sigma(n) + 9 is a perfect square.

10, 12, 27, 38, 90, 95, 110, 114, 142, 152, 230, 344, 356, 395, 442, 474, 639, 684, 738, 973, 1098, 1349, 1558, 1562, 1566, 1956, 2365, 2392, 2408, 2438, 2451, 2484, 2492, 2666, 2838, 3145, 3236, 3377, 3730, 3774, 3886, 4448, 4833, 5356

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..210

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

Mathematica

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

Prog

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

Crossrefs

Sequence in context: A108901 A073083 A129508 * A080470 A087217 A044972

Adjacent sequences: A015725 A015726 A015727 * A015729 A015730 A015731

Keyword

nonn

Author

Robert G. Wilson v

Status

approved