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Search: id:A110603
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| A110603 |
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Numbers n whose base 5 representations, interpreted as base 10 integers, are semiprimes. |
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+0
7
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| 4, 5, 9, 11, 12, 18, 19, 31, 36, 37, 38, 43, 44, 46, 47, 48, 51, 52, 53, 58, 59, 61, 76, 77, 78, 84, 86, 88, 94, 96, 103, 106, 108, 112, 128, 131, 146, 147, 148, 151, 156, 159, 161, 168, 171, 172, 177, 178, 181, 184, 194, 196, 198, 208, 212, 218, 223, 226, 227, 228
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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A108873 is the equivalent using base 3. A110602 is the equivalent using base 4. A110604 is the equivalent using base 6. A110605 is the equivalent using base 7. A110606 is the equivalent using base 8. A110607 is the equivalent using base 9.
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EXAMPLE
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a(1) = 4 because 4 (base 5) = 4, and 4 (base 10) = 2 * 2, a semiprime (A001358).
a(2) = 5 because 5 (base 5) = 10, and 10 (base 10) = 2 * 5.
a(3) = 9 because 9 (base 5) = 14, and 14 (base 10) = 2 * 7.
a(4) = 11 because 11 (base 5) = 21, and 21 (base 10) = 3 * 7.
a(5) = 12 because 12 (base 5) = 22, and 22 (base 10) = 2 * 11.
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MATHEMATICA
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Select[Range[228], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 5]]] == 2 &] (*Chandler*)
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CROSSREFS
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Cf. A001358, A007091, A108873, A110602, A110604, A110605, A110606, A110607.
Adjacent sequences: A110600 A110601 A110602 this_sequence A110604 A110605 A110606
Sequence in context: A067261 A001161 A099539 this_sequence A010416 A134921 A117870
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KEYWORD
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base,easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Jul 30 2005
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EXTENSIONS
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Corrected and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Aug 05 2005
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