A056917 Numbers n such that sigma(n)-phi(n) is a perfect square.

1, 15, 30, 44, 65, 77, 78, 87, 105, 141, 147, 186, 242, 247, 282, 301, 330, 335, 345, 450, 481, 560, 570, 589, 591, 606, 671, 705, 717, 767, 777, 785, 819, 820, 870, 1007, 1032, 1056, 1071, 1102, 1167, 1173, 1185, 1230, 1247, 1271, 1351, 1374, 1415, 1416, 1501

Offset

1,2

Links

Eric M. Schmidt, Table of n, a(n) for n = 1..1000

Example

sigma(44)-phi(44) = 84 - 20 = 8^2, so 44 is a term of the sequence.

Mathematica

Select[Range[10^3], IntegerQ[Sqrt[DivisorSigma[1, # ] - EulerPhi[ # ]]] &]

Prog

(PARI) isok(n) = issquare(sigma(n) - eulerphi(n)); \\ Michel Marcus, Oct 19 2016

Crossrefs

Sequence in context: A060700 A167210 A131933 * A344332 A044855 A044900

Adjacent sequences: A056914 A056915 A056916 * A056918 A056919 A056920

Keyword

easy,nonn

Author

Joseph L. Pe, Feb 12 2002

Extensions

More terms from Eric M. Schmidt, Oct 19 2016

Status

approved