Revision History for A057654
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#6 by N. J. A. Sloane at Tue Feb 11 19:05:22 EST 2014
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| AUTHOR
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_Joseph L. Pe (joseph_l_pe(AT)hotmail.com), _, Feb 12 2002
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Discussion
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| Tue Feb 11
| 19:05
| OEIS Server: https://oeis.org/edit/global/2119
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#5 by Bruno Berselli at Fri Jun 29 04:47:37 EDT 2012
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#4 by Donovan Johnson at Fri Jun 29 04:29:21 EDT 2012
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#3 by Donovan Johnson at Fri Jun 29 04:27:31 EDT 2012
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| NAME
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Numbers n such that sigma(n)^2- - phi(n)^2 is a perfect square.
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| DATA
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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, 10877, 12535, 13184, 13253, 14344, 14535, 16965, 18405, 19493, 19836
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| LINKS
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Donovan Johnson, <a href="/A057654/b057654.txt">Table of n, a(n) for n = 1..1000</a>
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| EXAMPLE
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sigma(95)^2- - phi(95)^2 = 120^2 - 72^2 = 96^2, so 95 is a term of the sequence.
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| STATUS
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approved
editing
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#2 by N. J. A. Sloane at Sat Jun 12 03:00:00 EDT 2004
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| NAME
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Numbers n such that sigma(n)^2-phi(n)^2 is a perfect square.
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| KEYWORD
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easy,nonn,new
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#1 by N. J. A. Sloane at Fri May 16 03:00:00 EDT 2003
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| NAME
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n such that sigma(n)^2-phi(n)^2 is a perfect square.
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| DATA
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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
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| OFFSET
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1,2
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| EXAMPLE
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sigma(95)^2-phi(95)^2 = 120^2 - 72^2 = 96^2, so 95 is a term of the sequence.
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| MATHEMATICA
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Select[Range[10^4], IntegerQ[Sqrt[DivisorSigma[1, # ]^2 - EulerPhi[ # ]^2]] &]
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| KEYWORD
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easy,nonn
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| AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 12 2002
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| STATUS
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approved
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