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 A324321 #9 Mar 14 2019 09:23:05 %S A324321 21,23,25,27,29,31,34,37,41,45,49,51,56,61,67,71,78,81,89,91,101,109, %T A324321 114,118,145,175,201,209,251,267,301,365,401,501,529,601,701,801,901, %U A324321 1001,1639,2001,3001,4001,5001,6001,7001,8001,9001,10001,20001,30001,40001 %N A324321 Numbers k such that Rd(k) == k (mod Ld(k)), where Rd(k) = A067079 and Ld(k) = A067080. %C A324321 All numbers of the form d*10^k+1, where d = 1,2,3,4,5,6,7,8,9 and k>0, are part of the sequence except 11. %e A324321 Rd(1639) = 1639*639*39*9 = 367609671, Ld(1639) = 1639*163*16*1 = 4274512 and 367609671 == 1639 (mod 4274512). %p A324321 op(select(n->n=mul(n mod 10^k, k=1..ilog10(n)+1) mod mul(trunc(n/10^k), k=0..ilog10(n)),[$1..40001])); %t A324321 Select[Range[10^5], Mod[Times @@ Map[FromDigits, NestWhileList[Rest@ # &, IntegerDigits@ #, Length@ # > 1 &]], Times @@ Map[FromDigits, NestWhileList[Most@ # &, IntegerDigits@ #, Length@ # > 1 &]]] == # &] (* _Michael De Vlieger_, Feb 25 2019 *) %Y A324321 Cf. A067079, A067080, A324322. %K A324321 nonn,easy %O A324321 1,1 %A A324321 _Paolo P. Lava_, Feb 22 2019