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A124602
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Position of the first 2 in the decimal expansion of the square root of n, or -1 if 2 never appears.
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0
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-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
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,3
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LINKS
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MATHEMATICA
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Table[Position[RealDigits[Sqrt[n], 10, 100][[1]], 2, 1, 1]/.{}->-1, {n, 0, 100}]//Flatten (* Harvey P. Dale, Aug 16 2022 *)
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PROG
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(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); }
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CROSSREFS
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KEYWORD
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base,easy,sign
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AUTHOR
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STATUS
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approved
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