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 A206287 #22 Dec 25 2024 21:01:25
%S A206287 1,11,13,17,19,101,103,107,109,113,121,127,131,137,139,143,149,151,
%T A206287 157,163,167,169,173,179,181,187,191,193,197,199,1009,1013,1019,1021,
%U A206287 1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1111
%N A206287 Numbers with all divisors starting with digit 1.
%C A206287 Equivalently, integers m with all divisors starting with the same first digit of m; in fact, as 1 divides all the integers, this digit is necessarily 1; also, for these terms m: A357299(m) = A000005(m). - _Bernard Schott_, Sep 25 2022
%H A206287 Robert Israel, <a href="/A206287/b206287.txt">Table of n, a(n) for n = 1..10000</a>
%e A206287 All divisors of 187 (1, 11, 17, 187) start with digit 1.
%p A206287 filter:= proc(n) andmap(t -> floor(t/10^ilog10(t)) = 1, numtheory:-divisors(n)) end proc:
%p A206287 select(filter, [seq($10^d .. 2*10^d-1, d=0..3)]); # _Robert Israel_, Dec 25 2024
%t A206287 fQ[n_] := Module[{d = Divisors[n]}, Union[IntegerDigits[#][[1]] & /@ d] == {1}]; Select[Range[1111], fQ] (* _T. D. Noe_, Feb 13 2012 *)
%Y A206287 Disjoint union of A045707 and A206288.
%Y A206287 Cf. A000005, A355592, A357299, A357300.
%Y A206287 Cf. A004615 (with last digit)
%K A206287 nonn,base
%O A206287 1,2
%A A206287 _Jaroslav Krizek_, Feb 12 2012