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%I #13 Sep 12 2017 13:29:32
%S 0,1,12,51,18426,69876,6168162,12105501,17759001,3008521945,
%T 100938635992,826471253301,3044088035830227,5889438558016867,
%U 55959294872171901
%N Pentagonal numbers not divisible by 10 whose reverse is triangular.
%e 51 is pentagonal and 15 is triangular
%t dtn[L_] := Fold[10#1+#2&, 0, L] tritest[n_] := Module[{t}, t=Floor[N[Sqrt[2n]]]; 2n==t(t+1)] A={0}; For[i=1, i>0, i++, t=i(3i-1)/2; r=dtn[Reverse[IntegerDigits[t]]]; If[tritest[r]&&Mod[t, 10]>0, AppendTo[A, t]; Print[A]]]
%t Select[Table[(n(3n-1))/2,{n,0,194*10^6}],Mod[IntegerReverse[#],10]!=0&&OddQ[Sqrt[8IntegerReverse[#]+1]]&] (* Requires Mathematica version 10 or later *) (* The program will take a long time to run *) (* _Harvey P. Dale_, Sep 12 2017 *)
%K base,more,nonn
%O 1,3
%A _Erich Friedman_, Jan 17 2002
%E a(13)-a(15) from _Lars Blomberg_, May 18 2011
%E Description clarified and offset corrected by _Lars Blomberg_, May 29 2011
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