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Least positive integer whose square root starts with just n odd decimal digits.
1

%I #11 Apr 18 2020 11:14:42

%S 4,1,10,3,63,129,91,1123,249,384,3131,391,2823,14293,9996,100603,

%T 17260,140863,999960,39984,1837521,11289570,999996,26336742,3999840,

%U 15999968,29116075,26824089,366858085,308642,99999996,314558578,6399999872,1599999968,381808465

%N Least positive integer whose square root starts with just n odd decimal digits.

%C We also have a(49) = 39999999984, a(54) = 3999999999840, a(59) = 3999999999984. - _Giovanni Resta_, Apr 18 2020

%H Giovanni Resta, <a href="/A334161/b334161.txt">Table of n, a(n) for n = 0..46</a>

%e Square root of first terms: 2, 1.0, 3.16, 1.732, 7.9372, 11.3578, ...

%o (PARI) a(n) = {my(g=10^n, v); for(k=1, oo, v=digits(floor(sqrt(k)*g))[1..n+1]; if(v[n+1]%2==0 && setintersect([1, 3, 5, 7, 9], v=Set(v[1..n]))==v, return(k))); }

%Y Cf. A210492, A333827.

%K nonn,base

%O 0,1

%A _Jinyuan Wang_, Apr 16 2020

%E Terms a(30) and beyond from _Giovanni Resta_, Apr 18 2020