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A114018
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Least n-digit prime whose digit reversal is also prime.
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9
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2, 11, 101, 1009, 10007, 100049, 1000033, 10000169, 100000007, 1000000007, 10000000207, 100000000237, 1000000000091, 10000000000313, 100000000000261, 1000000000000273, 10000000000000079, 100000000000000049, 1000000000000002901, 10000000000000000051
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OFFSET
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1,1
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COMMENTS
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The more compact version A168159 gives many more terms, cf. formula. [M. F. Hasler, Nov 21 2009]
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LINKS
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FORMULA
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MATHEMATICA
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f[n_] := Block[{k = 10^(n - 1)}, While[ !PrimeQ[k] || !PrimeQ[FromDigits@Reverse@IntegerDigits@k], k++ ]; k]; Array[f, 19] (* Robert G. Wilson v, Nov 19 2005 *)
lndp[n_]:=Module[{p=NextPrime[10^n]}, While[CompositeQ[IntegerReverse[ p]], p = NextPrime[ p]]; p]; Array[lndp, 20, 0] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 05 2019 *)
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PROG
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(PARI) for(x=1, 1e99, until( isprime(x=nextprime(x+1)) & isprime(eval(concat(vecextract(Vec(Str(x)), "-1..1")))), ); print1(x", "); x=10^#Str(x)-1) \\ M. F. Hasler, Nov 21 2009
(Python)
from sympy import isprime
def c(n): return isprime(n) and isprime(int(str(n)[::-1]))
def a(n): return next(p for p in range(10**(n-1), 10**n) if c(p))
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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