A124605 Position of the first 5 in the decimal expansion of the square root of n, or -1 if 5 never appears.

-1, -1, 8, 6, -1, 37, 31, 4, 36, -1, 26, 12, 10, 4, 6, 19, -1, 7, 16, 3, 7, 2, 7, 4, 10, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, 8, 18, 19, 5, 38, 22, 2, 8, 23, 13, 3, 13, -1, 13, 11, 8, 14, 14, 13, 11, 2, 4, 7, 4, 10, 22, 6, -1, 6, 13, 4, 9, 18, 10, 15, 4, 2, 7, 6, 45, 35, 18, 13, 15, -1, 3, 8, 4, 5, 10, 9, 8, 12, 11, 2, 2, 6, 4, 39, 6, 6, 16, 17, -1

Offset

0,3

Links

Robert Israel, Table of n, a(n) for n = 0..10000

Maple

f:= proc(n) uses StringTools; local d, S, r;
  if issqr(n) then
     S:= convert(sqrt(n), string);
     r:= Search("5", S);
     if r = 0 then -1 else r fi
  else
     d:= 10:
     do
       S:= convert(floor(10^d*sqrt(n)), string);
       r:= Search("5", S);
       if r > 0 then return r fi;
       d:= 2*d;
     od;
  fi
end proc:
map(f, [$0..100]); # Robert Israel, May 19 2019

Prog

(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); }

Crossrefs

Sequence in context: A113212 A275008 A070483 * A272430 A021120 A021541

Adjacent sequences: A124602 A124603 A124604 * A124606 A124607 A124608

Keyword

base,easy,sign,look

Author

Cino Hilliard, Dec 22 2006, corrected Jul 18 2007

Status

approved