A114079 Numbers k such that sigma(k)*phi(k)*k is a square.

1, 6, 40, 84, 162, 672, 2268, 2480, 3159, 18144, 58752, 80262, 91000, 126360, 140800, 170688, 358668, 634725, 718848, 1063300, 1089270, 1255338, 1701000, 2319525, 2869344, 4189500, 4608576, 5642000, 7834320, 8506400, 9450000, 10480640, 15049125, 17716608, 18674500

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..100

Example

sigma(84)*phi(84)*84 = 451584 = 672^2.

Mathematica

Select[Range[10^5], IntegerQ @ Sqrt[# * EulerPhi[#] * DivisorSigma[1, #]] &] (* Amiram Eldar, Aug 13 2019 *)

Prog

(PARI) isok(n) = issquare(sigma(n)*eulerphi(n)*n); \\ Michel Marcus, Aug 13 2019

Crossrefs

Cf. A000010, A000203.

Sequence in context: A200945 A217074 A110424 * A211065 A002595 A263956

Adjacent sequences: A114076 A114077 A114078 * A114080 A114081 A114082

Keyword

nonn

Author

Giovanni Resta, Feb 13 2006

Extensions

More terms from Amiram Eldar, Aug 13 2019

Status

approved