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A210492
Least nonsquare whose square root starts with just n even decimal digits.
3
2, 17, 5, 6, 37, 65, 8, 689, 1817, 18, 1652, 2135, 40886, 40332, 78740, 80661, 214227, 165389, 239008, 686015, 4260196, 5035566, 21402156, 7955040, 5018507, 408380425, 400339626, 514413258, 1767402369, 43624023, 40838115321, 2118615505, 49670344597, 43298228708
OFFSET
0,1
COMMENTS
a(29) = 43624023.
LINKS
MATHEMATICA
f[n_] := Block[{s = Split[ Boole[ EvenQ@# & /@ RealDigits[Sqrt@ n, 10, 32][[1]]]][[1]]}, If[IntegerQ@ Sqrt@ n || Union@ s == {0}, -1, Length@ s]]; t = Table[0, {30}]; k = 2; While[k < 100000001, a = f@ k; If[t[[a]] == 0, t[[a]] = k; Print[{a, k}]]; k++]; t
PROG
(PARI) a(n) = {my(g=10^n, v); for(k=2, oo, v=digits(floor(sqrt(k)*g))[1..n+1]; if(v[n+1]%2 && setintersect([0, 2, 4, 6, 8], v=Set(v[1..n]))==v && !issquare(k), return(k))); } \\ Jinyuan Wang, Apr 16 2020
CROSSREFS
Cf. A220426.
Sequence in context: A293179 A144212 A186683 * A355555 A370111 A057280
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
a(25) from Jinyuan Wang, Apr 16 2020
a(25) corrected and more terms from Giovanni Resta, Apr 18 2020
STATUS
approved