Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #15 Feb 16 2024 01:35:46
%S 7,77,1771,178871,1788888871,2188118778118812,
%T 218811879999999978118812,2188118799999999999999999999999978118812
%N a(1) = 7, a(n) = smallest palindromic nontrivial multiple of a(n-1) containing all decimal digits of a(n-1).
%C Differs from A082782 at a(6).
%C a(n) <= (10^A055642(a(n-1))+1)*a(n-1).
%C If a(n-1) > 10 and the last digit of a(n-1) <= 4, then a(n) <= (10^(A055642(a(n-1))-1)+1)*a(n-1).
%C For n=6..8, a(n) = 196930692 * A002275(2^(n-3)), and it follows that a(9) <= 196930692 * A002275(64). Conjecture: for all n >= 6, a(n) = 196930692 * A002275(2^(n-3)). Note that 196930692 is a term of A370052 and A370053. - _Max Alekseyev_, Feb 15 2024
%e a(3) = 1771 is a palindromic multiple of a(2) = 77 and contains two '7', all the digits of a(2).
%Y Cf. A055642, A082782, A342232, A342233, A342345, A342346, A370052, A370053.
%K nonn,base,more
%O 1,1
%A _Chai Wah Wu_, Mar 08 2021
%E a(8) from _Max Alekseyev_, Feb 15 2024