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A048347 a(n)^2 is the smallest square containing exactly n 2's. 1

%I

%S 5,15,149,1415,4585,14585,105935,364585,3496101,4714045,34964585,

%T 149305935,1490725415,4714469665,1490711985,149071333335,

%U 1105537083332,1489973900149,15106363633335,47140462469223

%N a(n)^2 is the smallest square containing exactly n 2's.

%C a(19) > 10^13. - _Jon E. Schoenfield_, Dec 25 2008

%C a(21) > 10^14. - _Giovanni Resta_, Jul 27 2018

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SquareNumber.html">Square Number</a>

%e From _Jon E. Schoenfield_, Dec 25 2008: (Start)

%e a(16) = 149071333335 = sqrt(22222262422274682222225);

%e a(17) = 1105537083332 = sqrt(1222212242622225512222224);

%e a(18) = 1489973900149 = sqrt(2220022223125222222222201). (End)

%e From _Giovanni Resta_, Jul 27 2018: (Start)

%e a(19) = 15106363633335 = sqrt(228202222222546222323222225);

%e a(20) = 47140462469223 = sqrt(2222223201812222222222223729). (End)

%t a[n_] := Block[{k=1}, While[DigitCount[k^2, 10, 2] != n, k++]; k]; Array[a, 7] (* _Giovanni Resta_, Jul 27 2018 *)

%Y Cf. A036509, A034980.

%K nonn,base,more

%O 1,1

%A _Patrick De Geest_, Mar 15 1999

%E a(13)-a(15) from _Max Alekseyev_, Oct 20 2008, Nov 10 2008, Dec 05 2008

%E a(16)-a(18) from _Jon E. Schoenfield_, Dec 25 2008

%E a(19)-a(20) from _Giovanni Resta_, Jul 27 2018

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Last modified March 3 04:02 EST 2021. Contains 341756 sequences. (Running on oeis4.)