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A238463
Numbers n such that phi(n) * sigma(n) + 1 is a perfect square.
1
2, 3, 5, 6, 7, 11, 13, 17, 19, 22, 23, 29, 31, 33, 37, 41, 43, 44, 47, 53, 59, 61, 67, 69, 71, 73, 76, 79, 82, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 140, 149, 151, 157, 163, 167, 173, 179, 181, 190, 191, 193, 197, 199, 211, 223, 227, 229
OFFSET
1,1
LINKS
MATHEMATICA
Select[Range[1000], IntegerQ[Sqrt[EulerPhi[#]DivisorSigma[1, #] + 1]]&]
PROG
(Magma) [n: n in [1..300] | IsSquare(EulerPhi(n) * SumOfDivisors(n) + 1)]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Mar 14 2014
STATUS
approved