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.
1, 21, 253, 1407, 3425, 17457, 17459, 933661, 1279313, 29581875, 47960915, 76385733, 158292295, 3222873413, 3817850653, 319145363229
Offset: 1
Examples
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.
Programs
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Maple
with(numtheory): P:=proc(q) global a,b,c,k,n,v; v:=[]; for n from 1 to q do a:=sort([op(divisors(n))]); b:=0; for k from 1 to nops(a) do c:=convert(a[-k],binary,decimal); b:=b*10^length(c)+c; od; if frac(convert(b,decimal,binary)/n)=0 then v:=[op(v),n]; fi; op(v); od; end: P(20000);
Extensions
a(9)-a(16) from Giovanni Resta, Dec 22 2024
Comments