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 A103576 Concatenations of pairs of primes that differ by 1000000. 2
 31000003, 371000037, 1511000151, 1931000193, 1991000199, 2111000211, 3131000313, 3671000367, 3971000397, 4091000409, 4571000457, 5411000541, 5471000547, 5771000577, 6191000619, 6911000691, 8291000829, 8591000859 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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. LINKS FORMULA a(n) = Concatenate(P, P+1000000) iff P prime and P+1000000 prime. EXAMPLE Prime(47) = 211 and 211 + 1000000 = Prime(78515) = 1000211. Concatenating these two primes gives 2111000211 = 3^4 * 17^2 * 31 * 2909. CROSSREFS Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719, A103523, A103534. Sequence in context: A297447 A205272 A261986 * A288087 A203276 A182088 Adjacent sequences: A103573 A103574 A103575 * A103577 A103578 A103579 KEYWORD base,easy,nonn AUTHOR Jonathan Vos Post, Mar 23 2005 STATUS approved

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Last modified March 22 18:49 EDT 2023. Contains 361433 sequences. (Running on oeis4.)