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Triangular numbers composed of digits {0,1,3}.
2

%I #15 Mar 31 2023 06:14:07

%S 1,3,10,300,3003,10011,303031,1010331,1030330,1313010,101111310,

%T 113033130,1033010331,11031100311,11033031331,31031010003,

%U 111111101310,313313301003,10113301131300,3330130113300130003,1113011003000100031311,11013033300110103011310

%N Triangular numbers composed of digits {0,1,3}.

%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr013.html">Tridigital Triangular Numbers</a>.

%F a(n) = A000217(A119036(n)). - _Tyler Busby_, Mar 31 2023

%t Rest[Select[FromDigits/@Tuples[{0, 1, 3}, 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 {0,1,3} where t is n*(n+1) div 2]; // _Vincenzo Librandi_, Dec 18 2015

%Y Cf. A000217, A119036. See A119033 for a table of cross-references.

%K nonn,base

%O 1,2

%A _Giovanni Resta_, May 10 2006

%E a(21)-a(22) from _Tyler Busby_, Mar 22 2023