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%I #11 Jun 17 2018 01:59:29
%S 31,11,2111,101111,311111,29111111,61111111,1711111111,14111111111,
%T 31111111111,311111111111,2111111111111,31111111111111,
%U 3511111111111111,5111111111111111,101111111111111111,3511111111111111111
%N a(n) is the first prime ending in exactly n 1's.
%H Harry J. Smith, <a href="/A065821/b065821.txt">Table of n, a(n) for n = 1..100</a>
%e a(4) = 101111 because 1111=11*101, 21111=3*31*227, 31111=53*587, 41111=7^2*829, 51111=3^4*631, 61111=23*2657, 71111=17*47*89, 81111=3*19*1423, 91111=179*509 so 101111 is the first prime ending in four 1's.
%t pe[n_]:=Module[{k=0,len=IntegerLength[n]},While[Mod[k,10]==1||(!PrimeQ[ k*10^len+n]),k++];k*10^len+n]; pe/@Table[(10^n-1)/9,{n,20}] (* _Harvey P. Dale_, Dec 31 2013 *)_
%o (PARI) { b=0; f=1; for (n=1, 100, b=10*b + 1; f*=10; k=0; while (!isprime(b + k*f), if (k%10, k++, k+=2)); write("b065821.txt", n, " ", b + k*f) ) } \\ _Harry J. Smith_, Nov 01 2009
%Y Cf. A037055, A065584, A065580, A065581, A065582.
%K base,nonn
%O 1,1
%A Jonathan Ayres (jonathan.ayres(AT)btinternet.com), Nov 23 2001
%E Edited and extended by _Robert G. Wilson v_, Jul 04 2003
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