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A089987
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Primes in the concatenation of consecutive numbers beginning with 2.
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6
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OFFSET
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1,1
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COMMENTS
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Sum of reciprocals = 0.5434783035011462065880780409...
23, 4567 and 89 are prime numbers, thus a(3) = A262571(9) = 23456789 is a prime obtained by concatenating 3 primes that are themselves the concatenation of consecutive integers. - XU Pingya, Apr 16 2017
No other primes less than the concatenation of 2,3,4,5,6,7,8,9,10,11,12,...,9999. - Robert Price, Nov 04 2018
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LINKS
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MATHEMATICA
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Select[Table[FromDigits[Flatten[IntegerDigits[Range[2, n]]]], {n, 2, 30}], PrimeQ[#] & ] (* Robert Price, Nov 05 2018 *)
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PROG
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(PARI) concatprime(n, p) = { sr=0; y=""; for(x=p, n, y=concat(Str(y), Str(x)); z=eval(y); if(ispseudoprime(z), print1(z", "); sr+=1./z; ); ); print(); print(sr) }
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CROSSREFS
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See also A007908 for the numbers 1234...n.
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KEYWORD
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nonn,base,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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