A119073 - OEIS

%I #21 Mar 30 2023 23:34:32

%S 6,66,406,666,66066,446040,600060,46046406,440466040,4040600460,

%T 6604444400406,4440066066400004040,644006046066000066046,

%U 44464646466606404046664666,464440406444064040044646006604604066,660466006640066446666000606004066646,60404640400640406040004460664400044060

%N Triangular numbers composed of digits {0,4,6}.

%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr046.html">Tridigital Triangular Numbers</a>.

%F a(n) = A000217(A119074(n)). - _Tyler Busby_, Mar 27 2023

%t Rest[Select[FromDigits/@Tuples[{0, 4, 6}, 10], IntegerQ[(Sqrt[8 # + 1] - 1)/2] &]] (* _Vincenzo Librandi_, Dec 18 2015 *)

%o (Magma) [t: n in [1..2*10^7] | Set(Intseq(t)) subset {0,4,6} where t is n*(n+1) div 2]; // _Vincenzo Librandi_, Dec 18 2015

%Y Cf. A000217, A058438, A119074.

%Y See A119033 for a table of cross-references.

%K nonn,base

%O 1,1

%A _Giovanni Resta_, May 10 2006

%E a(15)-a(16) from _Max Alekseyev_, May 10 2009

%E a(17) from _Tyler Busby_, Mar 27 2023