A124602 Position of the first 2 in the decimal expansion of the square root of n, or -1 if 2 never appears.

-1, -1, 5, 4, 1, 1, 1, 1, 1, -1, 4, 6, 25, 8, 28, 4, -1, 3, 2, 19, 4, 4, 12, 9, 34, -1, 13, 7, 2, 20, 5, 10, 8, 7, 25, 19, -1, 4, 10, 2, 3, 6, 17, 9, 5, 5, 4, 18, 3, -1, 17, 6, 2, 2, 8, 16, 16, 11, 17, 27, 10, 5, 31, 5, -1, 4, 3, 7, 2, 6, 8, 3, 5, 27, 4, 5, 32, 13, 12, 33, 5, -1, 18, 14, 56, 2, 2, 3, 23, 10, 7, 7, 12, 13, 13, 35, 13, 18, 24, 26, -1

Offset

0,3

Links

Table of n, a(n) for n=0..100.

Mathematica

Table[Position[RealDigits[Sqrt[n], 10, 100][[1]], 2, 1, 1]/.{}->-1, {n, 0, 100}]//Flatten (* Harvey P. Dale, Aug 16 2022 *)

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: A199453 A245699 A115637 * A320060 A132707 A213658

Adjacent sequences: A124599 A124600 A124601 * A124603 A124604 A124605

Keyword

base,easy,sign

Author

Cino Hilliard, Dec 22 2006, corrected Jul 18 2007

Status

approved