A054211 Numbers k such that k concatenated with k-1 is prime.

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

Author

Patrick De Geest, Feb 15 2000

Keywords

• nonn
• base
• nice

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

Crossrefs

Cf. A052089, A030457, A030458, A052087, A052088.

Cf. A010051, A068700 (subsequence), A127423.

Programs

Haskell

a054211 n = a054211_list !! (n-1)
a054211_list = filter ((== 1) . a010051' . a127423) [1..]
-- Reinhard Zumkeller, Jun 27 2015 Jul 15 2012

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 *)

PARI

isok(n) = isprime(eval(Str(n, n-1))); \\ Michel Marcus, Oct 14 2016