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Search: id:A122183
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| A122183 |
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Primes p_i by index i for which the period length of 1/p_i is a semiprime. |
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+0
2
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| 4, 6, 9, 11, 14, 15, 17, 19, 20, 26, 27, 34, 39, 41, 43, 56, 59, 61, 62, 64, 76, 83, 85, 86, 96, 101, 102, 109, 111, 112, 119, 124, 138, 140, 144, 147, 149, 150, 154, 161, 166, 168, 170, 171, 175, 192, 198, 203, 216, 219, 222, 224, 225, 235, 236, 239, 240, 246, 251
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Semiprime analogue of A072859 based on A002371.
Numbers n such that A002371(n) is an element of A001358.
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EXAMPLE
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a(1) = 4 because A002371(4) Period of decimal expansion of 1/(4th prime) = 6 = 2*3, a semiprime.
a(2) = 6 because A002371(6) = 6 = 2*3.
a(3) = 9 because A002371(9) = 22 = 2*11.
a(4) = 11 because A002371(11) = 15 = 3*5.
a(5) = 14 because A002371(14) = 21 = 3*7.
a(6) = 15 because A002371(15) = 46 = 2*23.
a(7) = 17 because A002371(17) = 58 = 2*29.
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MATHEMATICA
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semiprimeQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; PrimePi /@ Select[Prime@ Range@ 254, semiprimeQ@ MultiplicativeOrder[10, # ] &] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A000040, A001358, A002371, A072859, A128948.
Sequence in context: A160531 A060106 A094550 this_sequence A133578 A010387 A010411
Adjacent sequences: A122180 A122181 A122182 this_sequence A122184 A122185 A122186
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KEYWORD
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base,easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), May 10 2007
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EXTENSIONS
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Edited, corrected and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), May 22 2007
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