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Search: id:A108638
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| A108638 |
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Semiprime plus its digits is semiprime. |
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+0
1
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| 15, 22, 26, 33, 38, 39, 49, 51, 55, 57, 74, 77, 115, 123, 129, 134, 145, 155, 161, 169, 178, 187, 202, 206, 213, 214, 221, 237, 254, 265, 274, 278, 291, 299, 301, 303, 309, 321, 327, 335, 361, 371, 377, 381, 382, 386, 411, 437, 445, 466, 478, 485, 497, 505
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Suprisingly there are only three(?) semiprimes sp, 10,14,15, such that sp minus its digits is semiprime.
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EXAMPLE
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15=3*5 and 15+1+5=21=3*7.
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MATHEMATICA
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Select[Range[500], Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[ #+Plus@@IntegerDigits[ # ]]==2&]
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CROSSREFS
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Sequence in context: A018888 A115174 A092783 this_sequence A076379 A038753 A006615
Adjacent sequences: A108635 A108636 A108637 this_sequence A108639 A108640 A108641
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KEYWORD
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nonn,base
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Jun 14 2005
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