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A054211
Numbers k such that k concatenated with k-1 is prime.
6
4, 10, 22, 24, 34, 42, 58, 70, 78, 88, 100, 102, 108, 112, 114, 124, 148, 154, 160, 172, 180, 192, 198, 202, 208, 210, 214, 238, 244, 262, 264, 268, 270, 282, 294, 300, 304, 312, 328, 330, 334, 340, 342, 354, 372, 384, 390, 394, 412, 414, 420, 424, 444, 454
OFFSET
1,1
COMMENTS
A010051(A127423(a(n))) = 1. - Reinhard Zumkeller, Jun 27 2015
All terms are even. - Michel Marcus, Oct 14 2016
LINKS
MATHEMATICA
ncpQ[{a_, b_}]:=PrimeQ[FromDigits[Flatten[IntegerDigits[{b, a}]]]]; Transpose[ Select[Partition[Range[500], 2, 1], ncpQ]][[2]] (* Harvey P. Dale, Nov 25 2012 *)
Select[Range[500], PrimeQ[#*10^IntegerLength[#-1]+#-1]&] (* Harvey P. Dale, Mar 16 2019 *)
PROG
(Haskell)
a054211 n = a054211_list !! (n-1)
a054211_list = filter ((== 1) . a010051' . a127423) [1..]
-- Reinhard Zumkeller, Jun 27 2015 Jul 15 2012
(PARI) isok(n) = isprime(eval(Str(n, n-1))); \\ Michel Marcus, Oct 14 2016
CROSSREFS
Cf. A010051, A068700 (subsequence), A127423.
Sequence in context: A369846 A227803 A109885 * A112770 A338910 A217514
KEYWORD
nonn,base,nice
AUTHOR
Patrick De Geest, Feb 15 2000
STATUS
approved