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A048054
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Number of n-digit reversible primes (emirps).
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25
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4, 9, 43, 204, 1499, 9538, 71142, 535578, 4197196, 33619380, 274932272, 2294771254, 19489886063, 167630912672, 1456476399463
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OFFSET
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1,1
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COMMENTS
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The count includes palindromes.
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LINKS
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Cécile Dartyge, Bruno Martin, Joël Rivat, Igor E. Shparlinski, and Cathy Swaenepoel, Reversible primes, arXiv:2309.11380 [math.NT], 2023. See p. 36.
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EXAMPLE
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2, 3, 5 and 7 are 1-digit reversible primes, so a(1)=4.
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MATHEMATICA
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Count[Range[10^(# - 1), 10^# - 1], n_ /; And[PrimeQ@ n, PrimeQ@ FromDigits@ Reverse@ IntegerDigits@ n]] & /@ Range@ 7 (* Michael De Vlieger, Jul 14 2015 *)
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PROG
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(Python)
from sympy import isprime, primerange
return len([p for p in primerange(10**(n-1), 10**n)
if isprime(int(str(p)[::-1]))]) # Chai Wah Wu, Aug 14 2014
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CROSSREFS
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KEYWORD
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base,nonn,more
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AUTHOR
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EXTENSIONS
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a(14)-a(15) from Cécile Dartyge, Bruno Martin, Joël Rivat, Igor E. Shparlinski, and Cathy Swaenepoel, Oct 05 2023
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STATUS
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approved
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