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A006567
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Emirps (primes whose reversal is a different prime).
(Formerly M4887)
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159
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13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157, 167, 179, 199, 311, 337, 347, 359, 389, 701, 709, 733, 739, 743, 751, 761, 769, 907, 937, 941, 953, 967, 971, 983, 991, 1009, 1021, 1031, 1033, 1061, 1069, 1091, 1097, 1103, 1109, 1151, 1153, 1181, 1193, 1201
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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A palindrome is a word that when written in reverse results in the same word. for example, "racecar" reversed is still "racecar". Related to palindromes are semordnilaps. These are words that when written in reverse result in a distinct valid word. For example, "stressed" written in reverse is "desserts". Not all words are palindromes or semordnilaps. While certainly not all numbers are palindromes, all non-palindromic numbers when written in reverse will form semordnilaps. Narrowing to primes brings back the same trichotomy as with words: some numbers are emirps, some numbers are palindromic primes, but some words are neither.
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REFERENCES
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M. Gardner, The Magic Numbers of Dr Matrix. Prometheus, Buffalo, NY, 1985, p. 230.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n = 1..10000
C. K. Caldwell, The Prime Glossary, emirp
Brady Haran and N. J. A. Sloane, What Number Comes Next? (2018), Numberphile video
Eric Weisstein's World of Mathematics, Emirp.
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MAPLE
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read("transforms") ; isA006567 := proc(n) local R ; if isprime(n) then R := digrev(n) ; isprime(R) and R <> n ; else false; end if; end proc:
A006567 := proc(n) option remember ; local a; if n = 1 then 13; else a := nextprime(procname(n-1)) ; while not isA006567(a) do a := nextprime(a) ; end do; return a; end if; end proc:
seq(A006567(n), n=1..120) ; # R. J. Mathar, May 24 2010
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MATHEMATICA
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fQ[n_] := Block[{idn = IntegerReverse@ n}, PrimeQ@ idn && n != idn]; Select[Prime@ Range@ 200, fQ] (* Santi Spadaro, Oct 14 2001 and modified by Robert G. Wilson v, Nov 08 2015 *)
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PROG
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(MAGMA) [ n : n in [1..1194] | n ne rev and IsPrime(n) and IsPrime(rev) where rev is Seqint(Reverse(Intseq(n))) ]; // Sergei Haller (sergei(AT)sergei-haller.de), Dec 21 2006
(PARI) is(n)=my(r=eval(concat(Vecrev(Str(n))))); isprime(r)&&r!=n&&isprime(n) \\ Charles R Greathouse IV, Nov 20 2012
(PARI) select( {is_A006567(n, r=fromdigits(Vecrev(digits(n))))=isprime(r)&&r!=n&&isprime(n)}, primes(200)) \\ M. F. Hasler, Jan 31 2020
(Haskell)
a006567 n = a006567_list !! (n-1)
a006567_list = filter f a000040_list where
f p = a010051' q == 1 && q /= p where q = a004086 p
-- Reinhard Zumkeller, Jul 16 2014
(Python)
from sympy import prime, isprime
A006567 = [p for p in (prime(n) for n in range(1, 10**6)) if str(p) != str(p)[::-1] and isprime(int(str(p)[::-1]))] # Chai Wah Wu, Aug 14 2014
(Python)
from sympy import isprime, nextprime
def emirps(start=1, end=float('inf')): # generator for emirps in start..end
p = nextprime(start-1)
while p <= end:
revp = int(str(p)[::-1])
if p != revp and isprime(revp): yield p
p = nextprime(p)
print(list(emirps(end=1201))) # Michael S. Branicky, Jan 24 2021
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CROSSREFS
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Cf. A003684, A007628 (subsequence), A046732, A048051, A048052, A048053, A048054, A048895, A004086 (read n backwards).
A007500 is the union of A002385 and this sequence.
Sequence in context: A180526 A161401 A225035 * A263240 A246043 A246045
Adjacent sequences: A006564 A006565 A006566 * A006568 A006569 A006570
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KEYWORD
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nonn,nice,easy,base
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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More terms from James A. Sellers, Jan 22 2000
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STATUS
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approved
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