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Search: id:A068014
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| A068014 |
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Nonprimes n such that 1+Phi[n] and -1+Sigma[1,n] are prime numbers. |
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+0
1
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| 6, 10, 14, 21, 26, 34, 38, 40, 46, 55, 57, 58, 60, 63, 74, 76, 86, 88, 93, 111, 114, 117, 118, 124, 126, 135, 145, 153, 158, 166, 178, 184, 186, 190, 194, 198, 206, 208, 209, 216, 221, 224, 230, 232, 238, 250, 252, 254, 260, 266, 270, 278, 280, 295, 297, 298
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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1+A000010(n) and -1+A000203(n) are primes but n is nonprime
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EXAMPLE
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n=38, Phi[38]+1=19 and Sigma[38]-1=1+2+19+39-1=59.
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MATHEMATICA
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Do[s=-1+DivisorSigma[1, n]; s1=1+EulerPhi[n]; If[PrimeQ[s]&&PrimeQ[s1]&&!PrimeQ[n], Print[{n, s1, s}]], {n, 1, 1000}] generates sequence and related primes too;
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CROSSREFS
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Cf. A000010, A000203, A066071-A066080.
Sequence in context: A060650 A068198 A064899 this_sequence A057885 A015812 A080784
Adjacent sequences: A068011 A068012 A068013 this_sequence A068015 A068016 A068017
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Feb 08 2002
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