A178318 - OEIS

%I #5 Jul 16 2014 15:40:20

%S 2,5,11,101,181,1051,1181,1201,1811,10151,11251,11551,12101,12211,

%T 12511,15121,18181,100151,100501,101501,101581,102001,102101,102181,

%U 102551,105211,105251,108881,110051,110581,110881,111521,111581,115021,115201

%N Primes which remain prime after reflection across a vertical line through the middle of the number (numbers are written as digital clock style numerals).

%C Apart from first two terms: subsequence of A208259. - _Reinhard Zumkeller_, Jul 16 2014

%H Reinhard Zumkeller, <a href="/A178318/b178318.txt">Table of n, a(n) for n = 1..1000</a>

%e For example 1051 becomes 1201 under this reflection and since these are both prime, these number are part of the sequence. Note that a number must be composed only of the digits 0,1,2,5,8 to qualify.

%o (Haskell)

%o import Data.List (intersect, genericIndex)

%o a178318 n = a178318_list !! (n-1)

%o a178318_list = 2 : 5 : filter f a062332_list where

%o    f p = null (show p `intersect` "34679") && a010051' (r 0 p) == 1

%o    r y 0 = y

%o    r y x = r (10 * y + genericIndex [0,1,5,0,0,2,0,0,8,0] d) x'

%o              where (x', d) = divMod x 10

%o -- _Reinhard Zumkeller_, Jul 16 2014

%Y Cf. A125308, A178317.

%Y Cf. A010051, A004086, A208259, A062332.

%K nonn,base

%O 1,1

%A _David Nacin_, May 24 2010