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Search: id:A098684
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| A098684 |
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Numbers n such that pi(n)=P(d_1!!)*P(d_2!!)*...*P(d_k!!) where d_1 d_2 ... d_k is the decimal expansion of n and P(i) is i-th prime. |
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+0
4
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| 10, 30, 123, 41402, 1400523, 3173000, 3173001, 3173010, 3173011, 351226103, 351226113, 351226130, 351226131
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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There are no further terms up to 35000000.
Contribution from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jun 01 2009: (Start)
If 10*n is in the sequence and 10*n+1 is comosite then 10*n+1 is also in the sequence.
There is no further term up to 1.5*10^10. (End)
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EXAMPLE
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3173011 is in the sequence because pi(3173011)=P(3!!)*P(1!!)*P(7!!)*P(0!!)*P(1!!)*P(1!!).
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MATHEMATICA
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Do[d=IntegerDigits[n]; k=Length[d]; If[PrimePi[n]== Product[Prime[d[[j]]!! ], {j, k}], Print[n]], {n, 35000000}]
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CROSSREFS
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Cf. A098683, A098685, A098686.
Sequence in context: A005052 A057344 A115134 this_sequence A064012 A063154 A100500
Adjacent sequences: A098681 A098682 A098683 this_sequence A098685 A098686 A098687
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KEYWORD
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base,more,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 24 2004
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EXTENSIONS
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More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jun 01 2009
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