A048352 a(n)^2 is the smallest square containing exactly n 7's.

24, 76, 424, 3576, 8819, 88924, 278874, 2116076, 8819154, 61463576, 277450424, 526087234, 1943470576, 21858013924, 199694210926, 260341642412, 3574601764924, 11156736878576, 27180356468924

Offset

1,1

Comments

a(20) > 10^14. - Giovanni Resta, Jul 27 2018

Links

Table of n, a(n) for n=1..19.

Eric Weisstein's World of Mathematics, Square Number

Mathematica

a[n_] := Module[{i = 1}, While[DigitCount[i^2][[7]] != n, i++ ]; i]; (* Sam Handler (sam_5_5_5_0(AT)yahoo.com), Aug 22 2006 *)

Crossrefs

Cf. A036514, A034990.

Sequence in context: A211588 A211596 A214397 * A144459 A290710 A206010

Adjacent sequences: A048349 A048350 A048351 * A048353 A048354 A048355

Keyword

nonn,base,more

Author

Patrick De Geest, Mar 15 1999

Extensions

a(13)-a(16) from Jon E. Schoenfield, Jan 24 2009

a(17)-a(19) from Giovanni Resta, Jul 27 2018

Status

approved