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Smallest triangular number containing exactly n 5's.
1

%I #12 Mar 22 2020 17:31:18

%S 15,55,5565,255255,12552555,585555531,5355555765,50525595555,

%T 5258558551555,555595555515,1551745755555555,39355555555552515,

%U 552550545955255555,13555559555595513555,455557505555605555585,5555558514557555255755,555457555855555784555355,505555585555455555505395

%N Smallest triangular number containing exactly n 5's.

%t nsmall = Table[Infinity, 20];

%t For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];

%t n0 = Count[IntegerDigits[p], 5];

%t If[nsmall[[n0]] > p, nsmall[[n0]] = p]];

%t ReplaceAll[nsmall, Infinity -> "?"] (* _Robert Price_, Mar 22 2020 *)

%Y Cf. A048360, A036517-A036526.

%K nonn,base

%O 1,1

%A _David W. Wilson_

%E a(13)-a(18) from _Giovanni Resta_, Oct 30 2019