A048349 a(n)^2 is the smallest square containing exactly n 4's.
2, 12, 38, 212, 2538, 6888, 66592, 210771, 2059962, 6696592, 21081538, 209868112, 664488107, 3800598038, 18613286762, 209820981888, 666669703412, 666516649788, 6666894662768, 49400874945738, 156347319914172, 210747466045038, 5868938950479212, 21081850261503238, 66666663966850212
Offset: 1
Links
- Eric Weisstein's World of Mathematics, Square Number
Programs
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Mathematica
a[n_] := Block[{k=1}, While[DigitCount[k^2, 10, 4] != n, k++]; k]; Array[a, 7] (* Giovanni Resta, Jul 27 2018 *)
Extensions
More terms from Jon E. Schoenfield, Jan 14 2009
a(17)-a(20) from Giovanni Resta, Jul 27 2018
a(21)-a(25) from Max Alekseyev, Mar 06 2025