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Search: id:A129336
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| A129336 |
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Digital clock semiprimes. |
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+0
1
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| 4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, 58, 106, 111, 115, 118, 119, 121, 122, 123, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 201, 202, 203, 205, 206, 209, 213, 214, 215, 217, 218, 219, 221, 226, 235, 237, 247
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Semiprime analogue of A050246. Semiprimes possible on a 24-hour digital clock, with no seconds. The largest value is 2359 = 7 * 337 because 23:59 is the largest 4-digit number that appears on a 24-hour digital clock. On a 24-hour digital clock, there are 211 possible prime values: how many semiprime values are there?
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LINKS
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Randall Munroe, Factoring the Time. The online comic xkcd.com has a digital clock factoring cartoon.
Eric Weisstein's World of Mathematics, Clock Prime.
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EXAMPLE
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253 is in the sequence because (see the comic) a character looks at a digital clock reading 2:53 and says: "253 is 11 x 23." That clock-time is a semiprime.
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CROSSREFS
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Cf. A001358, A050246, A118848, A118849, A118850.
Sequence in context: A063762 A001358 A108764 this_sequence A103607 A108574 A046368
Adjacent sequences: A129333 A129334 A129335 this_sequence A129337 A129338 A129339
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KEYWORD
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base,easy,fini,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), May 27 2007
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