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A103576
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Concatenations of pairs of primes that differ by 1000000.
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2
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31000003, 371000037, 1511000151, 1931000193, 1991000199, 2111000211, 3131000313, 3671000367, 3971000397, 4091000409, 4571000457, 5411000541, 5471000547, 5771000577, 6191000619, 6911000691, 8291000829, 8591000859
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| After the first element, 31000003, which is prime, integers in this sequence can never be prime, as they are all multiples of 3. They can be semiprimes, as is the case for 3671000367 = 3 x 1223666789, 4571000457 = 3 x 1523666819, 5411000541 = 3 x 1803666847, 9071000907 = 3 x 3023666969.
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FORMULA
| a(n) = Concatenate(P, P+1000000) iff P prime and P+1000000 prime.
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EXAMPLE
| Prime(47) = 211 and 211 + 1000000 = Prime(78515) = 1000211. Concatenating these two primes gives 2111000211 = 3^4 * 17^2 * 31 * 2909.
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CROSSREFS
| Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719, A103523, A103534.
Sequence in context: A204346 A156420 A205272 * A203276 A125574 A151621
Adjacent sequences: A103573 A103574 A103575 * A103577 A103578 A103579
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KEYWORD
| base,easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 23 2005
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