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A057654 Numbers n such that sigma(n)^2-phi(n)^2 is a perfect square. 0
1, 95, 99, 146, 323, 377, 1095, 1102, 1351, 1368, 1630, 1919, 1943, 2261, 2639, 2743, 3915, 4607, 4743, 5042, 5045, 5183, 5249, 6347, 6497, 7389, 8265, 8307, 8749, 9407, 9701 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

EXAMPLE

sigma(95)^2-phi(95)^2 = 120^2 - 72^2 = 96^2, so 95 is a term of the sequence.

MATHEMATICA

Select[Range[10^4], IntegerQ[Sqrt[DivisorSigma[1, # ]^2 - EulerPhi[ # ]^2]] &]

CROSSREFS

Sequence in context: A067266 A171403 A055467 * A181767 A046005 A045121

Adjacent sequences:  A057651 A057652 A057653 * A057655 A057656 A057657

KEYWORD

easy,nonn

AUTHOR

Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 12 2002

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Last modified February 13 08:12 EST 2012. Contains 205451 sequences.