This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A330290 #8 Dec 09 2019 23:24:20 %S A330290 1,1,11,101,3,9,7,61,1821477701,311,449,89,29,37,121,349,1047,73,2741, %T A330290 59,5527,21,487,3679724250117316595527,137,257,33,99,27,47,17,19,13, %U A330290 39,63,23,557,53,159,117,351,81,3439913,677,83,197,151,453,211,1033,239296537198126662281,167,501 %N A330290 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 A330290 The next term a(54) requires the factorization of a composite 177 digit number 22177...67001. %e A330290 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 A330290 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 A330290 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 A330290 Cf. A020639, A000040, A000005, A330291, A330293, A240588. %K A330290 nonn,more,hard,base %O A330290 1,3 %A A330290 _Scott R. Shannon_, Dec 09 2019