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 A066757 Pentagonal numbers not divisible by 10 whose reverse is triangular. 0

%I

%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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