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 A104873 Concatenations of pairs of primes that differ by 10^12. 1
 611000000000061, 1631000000000163, 1931000000000193, 2111000000000211, 2711000000000271, 3311000000000331, 5471000000000547, 6611000000000661, 7511000000000751, 7871000000000787, 9971000000000997, 10511000000001051 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Integers in this sequence can never be prime, as they are all multiples of 3. They can be semiprimes, as is the case for Prime(177) concatenated with Prime(37607912056) = 10511000000001051 = 3 * 3503666666667017. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 FORMULA a(n) = Concatenate(P, P+10^12) iff P prime and P+10^12 prime. EXAMPLE 61 is prime, specifically prime(18) and 61 + 10^12 is prime, specifically prime(7607912020), so their concatenation is in this sequence: 611000000000061. The concatenation is not itself prime, as it equals 3 * 7 * 23 * 1265010351967. MATHEMATICA #*10^13+10^12+#&/@Select[Prime[Range[200]], PrimeQ[#+10^12]&] (* Harvey P. Dale, Jan 18 2021 *) CROSSREFS Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719, A103523, A103534, A103576, A103617. Sequence in context: A172601 A086438 A261149 * A297450 A172585 A336968 Adjacent sequences: A104870 A104871 A104872 * A104874 A104875 A104876 KEYWORD base,easy,nonn AUTHOR Jonathan Vos Post, Mar 29 2005 STATUS approved

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Last modified January 26 17:20 EST 2023. Contains 359833 sequences. (Running on oeis4.)