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A054211 Numbers n such that n concatenated with n-1 is prime. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A010051(A127423(a(n))) = 1. - Reinhard Zumkeller, Jun 27 2015

All terms are even. - Michel Marcus, Oct 14 2016

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

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. A052089, A030457, A030458, A052087, A052088.

Cf. A010051, A068700 (subsequence), A127423.

Sequence in context: A290998 A227803 A109885 * A112770 A217514 A235142

Adjacent sequences:  A054208 A054209 A054210 * A054212 A054213 A054214

KEYWORD

nonn,base,nice

AUTHOR

Patrick De Geest, Feb 15 2000

STATUS

approved

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Last modified October 20 20:24 EDT 2019. Contains 328273 sequences. (Running on oeis4.)