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Search: id:A118690
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| A118690 |
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Semiprimes for which both the sum and the product of the digits is also a semiprime. |
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+0
1
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| 4, 6, 9, 22, 33, 55, 77, 91, 123, 141, 177, 213, 217, 321, 411, 717, 721, 771, 1135, 1157, 1315, 1351, 1513, 1517, 1751, 3151, 5131, 5311, 7115, 11157, 11215, 11521, 11611, 11751, 12115, 12151, 15117, 15711, 17151, 21151, 51211, 57111, 61111, 75111
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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91 is in the sequence because (1) it is a semiprime, (2) the sum of its digits is 9+1=10, (3) the product of its digits is 1*9=9 and (4) both 9 and 10 are semiprimes.
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MATHEMATICA
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spQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; fQ[n_] := Block[{id = IntegerDigits@n}, spQ@n && spQ[Plus @@ id] && spQ[Times @@ id]]; Select[ Range@111172, fQ@# &] - Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 15 2006
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CROSSREFS
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Cf. A001358.
Adjacent sequences: A118687 A118688 A118689 this_sequence A118691 A118692 A118693
Sequence in context: A137253 A035135 A046338 this_sequence A084994 A046328 A046376
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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 15 2006
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