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A309935
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Primes p such that the base-10 concatenation (p+1)||p is prime.
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4
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3, 23, 41, 101, 107, 113, 179, 191, 197, 263, 269, 281, 293, 311, 353, 383, 389, 419, 443, 491, 521, 569, 659, 683, 701, 761, 773, 809, 821, 839, 881, 887, 911, 947, 1109, 1217, 1223, 1229, 1433, 1481, 1499, 1559, 1667, 1697, 1811, 1901, 1973, 2069, 2087, 2099, 2111, 2129
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(3) = 41 is in the sequence because 41 and 4241 are primes.
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MAPLE
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select(t -> isprime(t) and isprime(10^(1+ilog10(t))*(t+1)+t), [$1..20000]);
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MATHEMATICA
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Select[Prime[Range[350]], PrimeQ[(#+1)10^IntegerLength[#]+#]&] (* Harvey P. Dale, May 07 2022 *)
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PROG
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(Magma) [p:p in PrimesUpTo(2200)| IsPrime(Seqint(Intseq(p) cat Intseq(p+1)))]; // Marius A. Burtea, Aug 23 2019
(PARI) isok(k) = isprime(k) && isprime(eval(Str(k+1, k))); \\ Jinyuan Wang, Aug 26 2019
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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