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 A124688 Position of the first n in the decimal expansion of the cube root of n, or -1 if the digits of n never appear. 1

%I

%S 1,1,2,11,5,7,17,11,-1,14,50,19,144,4,5,29,56,228,164,13,35,33,161,62,

%T 377,58,60,-1,164,17,69,1,154,46,93,229,54,103,134,2,88,347,53,22,71,

%U 211,15,68,37,718,74,26,68,77,42,43,35,241,188,90,25,212,85,13,-1,22,165,14,260,82,44,33,36,176,66,26,40,17,58,72,9,156

%N Position of the first n in the decimal expansion of the cube root of n, or -1 if the digits of n never appear.

%H Chai Wah Wu, <a href="/A124688/b124688.txt">Table of n, a(n) for n = 0..10000</a>

%e For n = 8, cube root of 8 = 2, so 8 never appears.

%e For n = 12, cube root of 12 =2.28942848510666...77233158752412..., the first 12 starts in position 144.

%e For n = 31, cube root of 31 = 3.1413806..., the first 31 start in position 1. a(10^(3m)) = 1. - _Chai Wah Wu_, Oct 15 2016

%o (PARI) digitposcbrt2(n) = \ First n in the cbrt expansion of n { local(x,y,r,dot); for(x=0,n, r = (x^(1/3)); if(iscube(x), y=find(Str(floor(r)),x), y=find(Str(r),x); dot=find(Str(r),"."); if(dot < y, y--); ); if(y, print1(y","),print1(-1",") ) ) } find(str,match) = \Return the position of the first occurrence of string \match in string str { local(lnm,lns,x,c,i); str=Str(str); \This allows leaving quotes off input match=Str(match); c=0; i=0; lns=length(str); lnm=length(match); if(lnm>1,i=1); x=1; while(x<=lns-lnm+1, if(mid(str,x,lnm)== match,break,x++); ); if(x>lns,return(0),return(x)) } mid(str,s,n) = \ Get a substring of length n from string str starting at position s in str. { local(v,ln,x,tmp); v =""; tmp = Vec(str); ln=length(tmp); for(x=s,s+n-1, v=concat(v,tmp[x]); ); return(v) } iscube(n) = { local(r); r = n^(1/3); if(floor(r+.5)^3== n,1,0) }

%K base,easy,sign

%O 0,3

%A _Cino Hilliard_, Dec 25 2006

%E Corrected a(27), a(31) and a(64) by _Chai Wah Wu_, Oct 15 2016

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)