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Search: id:A118697
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| A118697 |
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Semiprimes with consecutive digits. |
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+0
2
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| 4, 6, 9, 10, 21, 34, 65, 87, 123, 321, 543, 789, 901, 1234, 4321, 8765, 34567, 56789, 98765, 654321, 876543, 901234, 1234567, 7654321, 7890123, 10987654, 21098765, 567890123, 12345678901, 54321098765, 76543210987, 87654321098
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Digits can be in ascending or descending order. After 9 comes 0.
The number of semiprimes with n consecutive digits: 3,5,5,3,3,3,3,2,1,0,4,0,2,0,2,1,1,1,1,0,1,2,0,1,0,0,2,1,0,0,1,1,1,0,0,0,0,2,1,0,1,0,0,0,2,1,0,0,0,0,..., . - Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 16 2006
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MATHEMATICA
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spQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; f[n_] := Block[{u = Range@n, d = Reverse@ Range@n, t = Table[1, {n}]}, Select[ Drop[ Union@ Flatten@ Table[ FromDigits /@ Mod[{u, d} + {i*t, i*t}, 10], {i, 10}], 2], spQ@# &]]; Array[f, 13] // Flatten - Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 16 2006
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CROSSREFS
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Cf. A001358.
Adjacent sequences: A118694 A118695 A118696 this_sequence A118698 A118699 A118700
Sequence in context: A108635 A071964 A135257 this_sequence A118695 A118693 A084668
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), May 20 2006
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 16 2006
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