%I #14 Aug 18 2020 05:40:34

%S 1,11,1101,110101,1101010001,110101000101,1101010001010001,

%T 110101000101000101,1101010001010001010001,

%U 1101010001010001010001000001,110101000101000101000100000101,110101000101000101000100000101000001

%N Binary strings that have 1's where primes occur, 0's elsewhere and every term ends with the n-th prime index.

%C a(2) and a(121) are primes. Are there any more?

%H Amiram Eldar, <a href="/A109227/b109227.txt">Table of n, a(n) for n = 1..168</a>

%e a(4) = 110101 because the string '00110101' has 1's at the prime indices 2,3,5,7 and the first two zeros are dropped.

%t a[n_] := FromDigits[Boole @ PrimeQ[Range[Prime[n]]]]; Array[a, 12] (* _Amiram Eldar_, Aug 18 2020 *)

%Y Cf. A109228.

%K base,easy,nonn

%O 1,2

%A _Jason Earls_, Jun 23 2005