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A015728
Numbers n such that phi(n) * sigma(n) + 9 is a perfect square.
2
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
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: A372488 A073083 A129508 * A080470 A087217 A044972
KEYWORD
nonn
STATUS
approved