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A066782
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Numbers n such that (n,EulerPhi(n)) lies on the hyperbola x^2 - y^2 = m^2, for some natural number m, i.e. n^2 - EulerPhi(n)^2 = m^2.
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1
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1, 5, 13, 25, 34, 41, 61, 68, 113, 125, 136, 169, 181, 219, 222, 272, 313, 390, 421, 444, 482, 544, 578, 613, 625, 657, 666, 761, 780, 888, 964, 979, 1013, 1088, 1156, 1170, 1201, 1301, 1332, 1560, 1681, 1741, 1776, 1861
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,1000
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EXAMPLE
| 5^2 - EulerPhi(5)^2 = 25 - 16 = 3^2, so 5 is a term of the sequence.
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MATHEMATICA
| Select[ Range[ 1, 10^4 ], IntegerQ[ Sqrt[ #^2 - EulerPhi[ # ]^2 ] ] & ]
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PROG
| (PARI) { n=0; for (m=1, 10^10, if (issquare(m^2 - eulerphi(m)^2), write("b066782.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 25 2010]
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CROSSREFS
| Sequence in context: A156679 A190618 A004627 * A094553 A094079 A194811
Adjacent sequences: A066779 A066780 A066781 * A066783 A066784 A066785
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 18 2002
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