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A124608 Position of the first 8 in the decimal expansion of the square root of n, or -1 if 8 never appears. 0

%I

%S -1,-1,19,8,-1,15,6,45,2,-1,13,17,18,15,9,2,-1,20,9,4,20,3,11,5,2,-1,

%T 15,17,15,3,26,11,5,13,2,9,-1,3,13,10,16,14,3,7,9,4,3,2,4,-1,8,7,16,3,

%U 4,7,3,5,11,3,14,2,2,23,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,-1,6,16,9,14,7,12,3,6,3,26,18,36,11,11,7,2,2,5,-1

%N Position of the first 8 in the decimal expansion of the square root of n, or -1 if 8 never appears.

%o (PARI) digitpos(n,m) = /* m-th digit in sqrt expansions */ { local(x,y,r,dot); default(realprecision,1000); for(x=0,n, r = sqrt(x); if(issquare(x), y=find(Str(floor(r)),m), y=find(Str(r),m); dot=find(Str(r),"."); if(dot < y, y--); ); if(y, print1(y","),print1(-1",") ) ) } find(str,match) = /* Revised 2007 */ { local(lnm,lns,tstr,vstr,x,j); vstr=Vec(Str(str)); match=Str(match); lns=length(str); lnm=length(match); for(x=1,lns-lnm+1, tstr=""; for(j=x,x+lnm-1, tstr=concat(tstr,vstr[j]); ); if(match==tstr,return(x)) ); return(0); }

%K base,easy,sign

%O 0,3

%A _Cino Hilliard_, Dec 22 2006, corrected Jul 18 2007

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Last modified June 22 02:16 EDT 2021. Contains 345367 sequences. (Running on oeis4.)