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A063466
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2*EulerPhi[n]+8-DivisorSigma[1,n] = 0.
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1
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6, 15, 21, 33, 39, 51, 57, 69, 87, 93, 111, 123, 129, 141, 159, 175, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 381, 393, 411, 417, 447, 453, 471, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717, 723, 753
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| Harry J. Smith, Table of n, a(n) for n=0,...,1000
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EXAMPLE
| If n=3p, where p is a prime other than 3, then 2*Phi[3p]=2(2p-2)=4.p-4, Sigma[3p]=4.p+4, 2Phi[3p]-Sigma[3p]+8=0. So 3p numbers are in the sequence. Also if n=175, Phi[175]=120,Sigma[175]=248, thus 2*Phi[175]-Sigma[175]+8=0, so 175 is here. Note that 175 is not of 3p form. No more such exotic term was found below 100000.
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PROG
| (PARI) { n=-1; for (m=1, 10^9, if (sigma(m) - 2*eulerphi(m) == 8, write("b063466.txt", n++, " ", m); if (n==1000, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 22 2009]
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CROSSREFS
| Sequence in context: A012412 A009092 A015793 * A138109 A072521 A130178
Adjacent sequences: A063463 A063464 A063465 * A063467 A063468 A063469
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jul 26 2001
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