A032695 - OEIS

%I #8 Apr 07 2015 15:32:42

%S 1,7,9,39,63,77,83,221,229,237,521,547,689,719,733,741,803,861,907,

%T 1283,1647,2003,2051,2073,2467,2727,3003,3063,3331,3487,3597,3609,

%U 3629,3719,3773,3857,3997,4421,4449,4499,4747,4919,5083,5439,5541

%N Exactly 5 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime.

%H Harvey P. Dale, <a href="/A032695/b032695.txt">Table of n, a(n) for n = 1..1000</a>

%e If a(n) = 77 then we find '2'77, '5'77, '6'77, '8'77 and '9'77 to be primes.

%t Select[Range[5600],Count[Table[n*10^IntegerLength[#]+#,{n,9}],_?PrimeQ] == 5&] (* _Harvey P. Dale_, Apr 07 2015 *)

%K nonn,base

%O 1,2

%A _Patrick De Geest_, May 15 1998