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%I #23 Jan 15 2023 01:08:37
%S 4,10,22,24,34,42,58,70,78,88,100,102,108,112,114,124,148,154,160,172,
%T 180,192,198,202,208,210,214,238,244,262,264,268,270,282,294,300,304,
%U 312,328,330,334,340,342,354,372,384,390,394,412,414,420,424,444,454
%N Numbers k such that k concatenated with k-1 is prime.
%C A010051(A127423(a(n))) = 1. - _Reinhard Zumkeller_, Jun 27 2015
%C All terms are even. - _Michel Marcus_, Oct 14 2016
%H Reinhard Zumkeller, <a href="/A054211/b054211.txt">Table of n, a(n) for n = 1..10000</a>
%t ncpQ[{a_,b_}]:=PrimeQ[FromDigits[Flatten[IntegerDigits[{b,a}]]]]; Transpose[ Select[Partition[Range[500],2,1],ncpQ]][[2]] (* _Harvey P. Dale_, Nov 25 2012 *)
%t Select[Range[500],PrimeQ[#*10^IntegerLength[#-1]+#-1]&] (* _Harvey P. Dale_, Mar 16 2019 *)
%o (Haskell)
%o a054211 n = a054211_list !! (n-1)
%o a054211_list = filter ((== 1) . a010051' . a127423) [1..]
%o -- _Reinhard Zumkeller_, Jun 27 2015 Jul 15 2012
%o (PARI) isok(n) = isprime(eval(Str(n, n-1))); \\ _Michel Marcus_, Oct 14 2016
%Y Cf. A052089, A030457, A030458, A052087, A052088.
%Y Cf. A010051, A068700 (subsequence), A127423.
%K nonn,base,nice
%O 1,1
%A _Patrick De Geest_, Feb 15 2000
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