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A066110
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Primes of form Sigma4(n)/Sigma2(n), arising in A066109.
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3
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13, 73, 313, 601, 28393, 83233, 922561, 3416953, 13842121, 47451433, 141146281, 212601841, 234750601, 294482761, 2750006041, 3262751521, 4362404353, 4784281393, 5236041961, 9354855121, 9597826993, 13564461457, 16936647121
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,250
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FORMULA
| Primes of form A001159[A066109(n)]/A001157[A066109(n)].
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EXAMPLE
| m=20: divisors[20]={20,10,5,4,2,1},Sigma4=160000+10000+625+256+16+1=170898, Sigma2=400+100+25+16+4+1=546; p=170898/546=73 is prime, the 2nd term.
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MATHEMATICA
| Do[s=DivisorSigma[4, n]; z=DivisorSigma[2, n]; If[PrimeQ[s/z], Print[{n, s, z, s/z}]], {n, 1, 10000000}] Output=s/z.
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PROG
| (PARI) { n=0; for (m=1, 10^9, if (frac(f=sigma(m, 4)/sigma(m, 2)), next); if (isprime(f), write("b066110.txt", n++, " ", f); if (n==250, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Feb 01 2010]
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CROSSREFS
| Cf. A001159, A001157, A000040, A066109-A066113.
Sequence in context: A143008 A107963 A006230 * A020527 A146618 A139157
Adjacent sequences: A066107 A066108 A066109 * A066111 A066112 A066113
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 05 2001
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