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%I #16 Nov 17 2019 15:43:56
%S -1,-1,12,2,-1,7,8,5,7,-1,6,8,13,9,2,3,-1,13,10,15,3,6,8,2,6,-1,14,11,
%T 28,10,3,4,23,2,18,6,-1,5,15,7,14,10,5,4,11,2,2,24,12,1,1,1,1,1,1,1,1,
%U 1,1,1,1,1,1,1,-1,7,47,8,26,15,14,8,9,8,10,10,2,2,5,10,6,-1,13,9,21,10,3,4,28,27,16,52,24,8,8,2,2,7,31,6,-1
%N Position of the first 7 in the decimal expansion of the square root of n, or -1 if 7 never appears.
%C There is only one number -- 20,976 -- out of the first 100,000 integers for which the term in this sequence is greater than 100. Its term is 133. - _Harvey P. Dale_, Nov 17 2019
%t Table[Position[RealDigits[Sqrt[n],10,200][[1]],7,1,1]/.{}->-1,{n,0,200}]//Flatten (* _Harvey P. Dale_, Nov 17 2019 *)
%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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