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A056917 Numbers n such that sigma(n)-phi(n) is a perfect square. 2
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 (list; graph; refs; listen; history; text; internal format)
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 * A044855 A044900 A008597

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

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Last modified November 20 12:13 EST 2019. Contains 329335 sequences. (Running on oeis4.)