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A221651 Numbers divisible by their first digit squared (excluding those whose first digit is 1).

%I A221651 #37 May 20 2013 01:43:25
%S A221651 20,24,28,36,48,50,200,204,208,212,216,220,224,228,232,236,240,244,
%T A221651 248,252,256,260,264,268,272,276,280,284,288,292,296,306,315,324,333,
%U A221651 342,351,360,369,378,387,396,400,416,432,448,464,480,496,500,525,550,575
%N A221651 Numbers divisible by their first digit squared (excluding those whose first digit is 1).
%C A221651 Numbers where  floor(n/10^floor(log(n)))^2 divides n.
%H A221651 Christian N. K. Anderson, <a href="/A221651/b221651.txt">Table of n, a(n) for n = 1..10000</a>
%H A221651 Christian N. K. Anderson, <a href="/A221651/a221651_1.gif">Ulam Spiral</a> for the first 10000 terms. [Draw the usual Ulam spiral, containing all the nonnegative integers, and color the numbers belonging to this sequence yellow]
%e A221651 48 is divisible by 4^2.
%o A221651 (R)
%o A221651 x=0; y=rep(0,1000); len=0
%o A221651 firstdig<-function(x) as.numeric(substr(as.character(x),1,1))
%o A221651 isint<-function(x) x==as.integer(x)
%o A221651 while(len<10000) if((fd=firstdig((x=x+1)))>1) if(isint(x/fd^2)) y[(len=len+1)]=x
%Y A221651 Cf. A132359, A034709, A034837, A005349, A007602, A034838, A225297, A225722, A225683.
%K A221651 nonn,base
%O A221651 1,1
%A A221651 _Kevin L. Schwartz_ and _Christian N. K. Anderson_, May 04 2013