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%I #10 Mar 25 2023 09:47:20
%S 1,91,1891,8911,188191,889111,899811,998991,1188111,11899881,88891111,
%T 1918188891,8888911111,9998888991,189889118191,191819818191,
%U 199198198891,888889111111,88888891111111,8888888911111111,888888889111111111,88888888891111111111
%N Triangular numbers composed of digits {1,8,9}.
%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr189.html">Tridigital Triangular Numbers</a>
%F a(n) = A000217(A119151(n)). - _Michel Marcus_, Mar 24 2023
%Y Cf. A000217, A053915, A119151. 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 24 2023
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