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A185867 Numbers m whose decimal digits are a subsequence of the decimal digits of k*m for some 1 < k < 10. 0

%I

%S 2,4,5,6,8,15,18,20,25,35,40,45,50,60,75,80,125,150,175,180,200,225,

%T 250,275,350,375,400,450,475,500,575,600,625,675,750,800,875,1125,

%U 1250,1375,1500,1625,1750,1800,1875

%N Numbers m whose decimal digits are a subsequence of the decimal digits of k*m for some 1 < k < 10.

%C Are there finitely many non-multiples of 10 in this sequence? a(72) = 7875 seems to be the last one. - _Charles R Greathouse IV_, Feb 08 2011

%e 15 is a term because 15*7 = 105, and 105 can be formed from 15 by inserting the digit 0 in the middle.

%o (PARI) sub(v,u)=my(j=1);if(#v==#u,return(0));for(i=1, #v, if(v[i]!=u[j],if(i!=j,return(0)),j++));1

%o isA185867(n)=my(N=eval(Vec(Str(n))));for(k=2, 9, if(sub(eval(Vec(Str(n*k))),N),return(k)));0

%K nonn,base

%O 1,1

%A _Paul Richards_, Feb 05 2011

%E Program and a(22)-a(45) from _Charles R Greathouse IV_, Feb 08 2011

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Last modified April 1 12:14 EDT 2023. Contains 361690 sequences. (Running on oeis4.)