A124604 - OEIS

%I #5 Oct 01 2013 21:35:19

%S -1,-1,2,23,-1,11,2,3,5,-1,27,7,2,11,3,9,1,1,1,1,1,1,1,1,1,-1,16,8,38,

%T 7,2,7,7,3,10,18,-1,25,4,3,4,2,2,5,6,11,22,7,19,-1,14,3,23,26,3,2,2,3,

%U 23,6,3,6,4,22,-1,9,4,14,3,16,12,2,2,3,12,7,15,4,15,7,3,-1,14,5,25,6,8,18,12,2,2,10,9,3,10,3,69,3,5,3,-1

%N Position of the first 4 in the decimal expansion of the square root of n, or -1 if 4 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