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Triangular numbers composed of digits {1,4,6}.
2

%I #15 Jun 20 2023 21:02:39

%S 1,6,66,666,6441,41616,146611,464166,1464616,4114146,14116641,

%T 664611111,1164441411,16646464416,41641661166,66114661161,

%U 144161141446,161646441166,1464464661166,4464411144441,44416146616416,61116114144646,466141616644641,1116644466666141,1161666441164166

%N Triangular numbers composed of digits {1,4,6}.

%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr146.html">Tridigital Triangular Numbers</a>

%F a(n) = A000217(A119126(n)). - _Michel Marcus_, Mar 22 2023

%t Table[Select[FromDigits/@Tuples[{1,4,6},n],OddQ[Sqrt[8#+1]]&],{n,16}]//Flatten (* _Harvey P. Dale_, Jun 20 2023 *)

%Y Cf. A000217, A027676, A119126. See A119033 for a table of cross-references.

%K nonn,base

%O 1,2

%A _Giovanni Resta_, May 10 2006

%E a(22)-a(24) from _Tyler Busby_, Mar 22 2023

%E a(25) from _Harvey P. Dale_, Jun 20 2023