cp's OEIS Frontend

A379170 Let m be the concatenation, in descending order, of the divisors of k written in base 2 and then converted in base 10. Sequence lists k which divide m.

%I A379170 #11 Jan 03 2025 02:04:41
%S A379170 1,21,253,1407,3425,17457,17459,933661,1279313,29581875,47960915,
%T A379170 76385733,158292295,3222873413,3817850653,319145363229
%N A379170 Let m be the concatenation, in descending order, of the divisors of k written in base 2 and then converted in base 10. Sequence lists k which divide m.
%C A379170 Tested up 4*10^11 by _Giovanni Resta_, Dec 22 2024
%e A379170 Divisors of 21 are 1, 3, 7, 21 which in base 2 are 1, 11, 111, 10101. Their concatenation is 10101111111 which in base 10 is 1407. Finally 1407/21 = 67 is an integer, so 21 is a member of the sequence.
%p A379170 with(numtheory): P:=proc(q) global a,b,c,k,n,v; v:=[];
%p A379170 for n from 1 to q do a:=sort([op(divisors(n))]); b:=0;
%p A379170 for k from 1 to nops(a) do c:=convert(a[-k],binary,decimal); b:=b*10^length(c)+c; od;
%p A379170 if frac(convert(b,decimal,binary)/n)=0 then v:=[op(v),n]; fi;
%p A379170 op(v); od; end: P(20000);
%Y A379170 Cf. A224930, A379169.
%K A379170 nonn,base,more
%O A379170 1,2
%A A379170 _Paolo P. Lava_, Dec 17 2024
%E A379170 a(9)-a(16) from  _Giovanni Resta_, Dec 22 2024