A330290 - OEIS

%I #8 Dec 09 2019 23:24:20

%S 1,1,11,101,3,9,7,61,1821477701,311,449,89,29,37,121,349,1047,73,2741,

%T 59,5527,21,487,3679724250117316595527,137,257,33,99,27,47,17,19,13,

%U 39,63,23,557,53,159,117,351,81,3439913,677,83,197,151,453,211,1033,239296537198126662281,167,501

%N a(1) = 1; for n > 1, a(n) = the smallest divisor of the number formed by the concatenation of a(1) to a(n-1) that has not previously appeared in the sequence.

%C The next term a(54) requires the factorization of a composite 177 digit number 22177...67001.

%e a(3) = 11 as the concatenation of a(1) and a(2) = '11' and 11, the smallest divisor of 11, has not appeared in the sequence.

%e a(4) = 101 as the concatenation of a(1)..a(3) is '1111' and 101 is the smallest divisor of 1111 which has not appeared in the sequence. Note that 11 also divides 1111 but a(3) = 11.

%e a(6) = 9 as the concatenation of a(1)..a(5) is '11111013' and 9 is the smallest divisor of 11111013 which has not appeared in the sequence. Note that 3 also divides 11111013 but a(5) = 3.

%Y Cf. A020639, A000040, A000005, A330291, A330293, A240588.

%K nonn,more,hard,base

%O 1,3

%A _Scott R. Shannon_, Dec 09 2019