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 A048347 a(n)^2 is the smallest square containing exactly n 2's. 1
 5, 15, 149, 1415, 4585, 14585, 105935, 364585, 3496101, 4714045, 34964585, 149305935, 1490725415, 4714469665, 1490711985, 149071333335, 1105537083332, 1489973900149, 15106363633335, 47140462469223 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(19) > 10^13. - Jon E. Schoenfield, Dec 25 2008 a(21) > 10^14. - Giovanni Resta, Jul 27 2018 LINKS Eric Weisstein's World of Mathematics, Square Number EXAMPLE From Jon E. Schoenfield, Dec 25 2008: (Start) a(16) = 149071333335 = sqrt(22222262422274682222225); a(17) = 1105537083332 = sqrt(1222212242622225512222224); a(18) = 1489973900149 = sqrt(2220022223125222222222201). (End) From Giovanni Resta, Jul 27 2018: (Start) a(19) = 15106363633335 = sqrt(228202222222546222323222225); a(20) = 47140462469223 = sqrt(2222223201812222222222223729). (End) MATHEMATICA a[n_] := Block[{k=1}, While[DigitCount[k^2, 10, 2] != n, k++]; k]; Array[a, 7] (* Giovanni Resta, Jul 27 2018 *) CROSSREFS Cf. A036509, A034980. Sequence in context: A207970 A207971 A245648 * A034980 A174850 A143048 Adjacent sequences:  A048344 A048345 A048346 * A048348 A048349 A048350 KEYWORD nonn,base,more AUTHOR Patrick De Geest, Mar 15 1999 EXTENSIONS a(13)-a(15) from Max Alekseyev, Oct 20 2008, Nov 10 2008, Dec 05 2008 a(16)-a(18) from Jon E. Schoenfield, Dec 25 2008 a(19)-a(20) from Giovanni Resta, Jul 27 2018 STATUS approved

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Last modified January 22 03:32 EST 2021. Contains 340360 sequences. (Running on oeis4.)