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 A368949 #9 Jan 20 2024 09:31:42 %S A368949 21,33,39,51,55,57,65,69,85,87,93,95,111,115,119,123,129,133,141,145, %T A368949 147,155,159,161,171,177,183,185,201,203,205,207,213,215,217,219,230, %U A368949 235,237,249,253,259,261,265,267,275,279,287,290,291,295,301,303,305,309,310,319,321,327,329,333,335,339,341 %N A368949 Complement of A368087 in A174905. %C A368949 A298855 is a subsequence, number 147 = 3 * 7^2 is the first entry in A368949 not in A298855. This sequence is a subsequence of A174905 = A241008 union A241010. %C A368949 Alternate definition: Every number n in this sequence has at least 2 distinct odd prime factors and its symmetric representation of sigma consists only of parts of width 1. %e A368949 21 is the smallest number in this sequence since 3 * 5 is not in A174905. %e A368949 The smallest number in this sequence with 3 distinct odd prime factors is 903 = 3*7*43 which has width pattern (A341969) 101010101010101 of length 17 since ... < d_i < 2 * d_i < d_(i+1) < 2 * d_(i+1) ... holds for all its divisors. %t A368949 (* a174905[ ] is defined in A174905 and propQ[ ] in A368087 *) %t A368949 a368949[m_, n_] := Select[Range[m, n], a174905[#]&&!propQ[#]&] %t A368949 a368949[1, 350] %Y A368949 Cf. A005279, A174905, A235791, A237048, A237270, A237593, A241008, A241010, A249223, A298855, A341969, A368087. %K A368949 nonn %O A368949 1,1 %A A368949 _Hartmut F. W. Hoft_, Jan 10 2024