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A103523
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Concatenations of pairs of primes that differ by 100.
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4
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3103, 7107, 13113, 31131, 37137, 67167, 73173, 79179, 97197, 127227, 139239, 151251, 157257, 163263, 181281, 193293, 211311, 283383, 331431, 349449, 367467, 379479, 409509, 421521, 457557, 463563, 487587, 499599, 541641, 547647, 577677
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Integers in this sequence can never be prime, as they are all multiples of 3. They can be semiprimes, as with the values for which the smaller prime P is prime(i) for i = 2, 12, 21, 22, 31, 36, 38, 42, 67, 70, 73, 75, 88, 93, 100, 101, 122, 131, 147, 157, ... For our example 9191019, note that 919 = Prime(157) and 1019 = Prime(186), hence since 1719191019 = 3 x 3063673 we list 157 in the indixes of semiprimes, above.
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FORMULA
| a(n) = Concatenate(P, P+100) iff P prime and P+100 prime.
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EXAMPLE
| 9191019 is in this sequence because 919 is prime, 919+100 = 1019 is prime and 9191019 is the concatenation of those two primes differing by 100.
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CROSSREFS
| Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719.
Sequence in context: A092129 A206132 A187305 * A090056 A187593 A137839
Adjacent sequences: A103520 A103521 A103522 * A103524 A103525 A103526
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KEYWORD
| base,easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 21 2005
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