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Brilliant numbers (A078972) whose digit reversal is a triangular number.
1

%I #9 Nov 21 2013 12:48:47

%S 6,10,649,1207,54253,56341,60391,66259,66331,101971,155143,166339,

%T 351433,672319,3003193,3054853,5043763,5631229,5858119,6163831,

%U 6256603,6462847,6473899,6556177,6687883,8210989,8236513,8735491,8788033,10716571,11576143

%N Brilliant numbers (A078972) whose digit reversal is a triangular number.

%e 649=11*59 is brilliant and 946=T(43).

%t bnoQ[n_]:=Module[{fi=FactorInteger[n],tfi,nn}, tfi=Transpose[fi]; Total[tfi[[2]]]==2 &&IntegerLength[First[tfi[[1]]]] == IntegerLength[Last[tfi[[1]]]]]; tnoQ[n_]:=IntegerQ[(Sqrt[1 +8FromDigits[ Reverse[IntegerDigits[n]]]]-1)/2]; Select[Select[Range[700000], bnoQ], tnoQ] (* _Harvey P. Dale_, Apr 17 2011 *)

%Y Cf. A078972, A115678.

%K nonn,base

%O 1,1

%A _Giovanni Resta_, Jan 31 2006

%E a(15)-a(31) from _Donovan Johnson_, Apr 26 2011