A114344 - OEIS

%I #18 Jun 18 2023 08:44:54

%S 1,1,5,3,-1,37,39,5,2,-1,89,20,52,222,319,49,-1,12,99,25,144,61,41,9,

%T 109,-1,145,10,268,33,189,184,155,371,45,108,-1,118,26,11,149,146,108,

%U 5,235,49,299,253,32,-1,103,212,120,179,353,119,225,64,10,108,104

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

%e For n=5, sqrt(5) = 2.23606797749978969640917366873127623544...

%e 5 occurs in the 37th position so 37 is the 6th entry in the table counting from the 0th entry.

%o (PARI) digitpos(n) = { local(x,y,r,dot); for(x=0,n, r=sqrt(x); if(issquare(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",") ) ) }

%o 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); }

%Y Cf. A002193, A002194, A002163, A010464, A010465, A010466, A010467.

%K base,easy,sign

%O 0,3

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