A210492 Least nonsquare whose square root starts with just n even decimal digits.

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

Giovanni Resta, Table of n, a(n) for n = 0..43

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

Adjacent sequences: A210489 A210490 A210491 * A210493 A210494 A210495

Keyword

nonn,base

Author

Robert Israel and Robert G. Wilson v, Jan 23 2013

Extensions

a(25) from Jinyuan Wang, Apr 16 2020

a(25) corrected and more terms from Giovanni Resta, Apr 18 2020

Status

approved