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%I #11 Apr 07 2022 14:59:33
%S 120,153,210,253,325,351,496,946,1378,1485,1830,1891,2145,2415,2701,
%T 3081,3570,3655,3741,3916,4095,4371,4560,4851,4950,5356,5460,5565,
%U 5778,6555,7021,7381,7503,7875,8911,9045,9316,10296,11325,11476,11935,12090
%N Triangular numbers that have some nontrivial permutation of digits which is also triangular.
%t tnpQ[n_]:=Module[{p=FromDigits/@Rest[Permutations[IntegerDigits[n]]],q},q= DeleteCases[ p,_?(IntegerLength[#]!=IntegerLength[n]&)];Count[q,_?(OddQ[ Sqrt[8#+1]]&)]>0]; Select[Accumulate[Range[200]],tnpQ]
%Y Cf. A000217.
%K nonn,base
%O 1,1
%A _Erich Friedman_
%E Offset set to 1 by _Sean A. Irvine_, Aug 20 2020