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 A066757 Pentagonal numbers not divisible by 10 whose reverse is triangular. 0
 0, 1, 12, 51, 18426, 69876, 6168162, 12105501, 17759001, 3008521945, 100938635992, 826471253301, 3044088035830227, 5889438558016867, 55959294872171901 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..15. EXAMPLE 51 is pentagonal and 15 is triangular MATHEMATICA 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]]] 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 *) CROSSREFS Sequence in context: A115680 A231298 A231359 * A225306 A331041 A317466 Adjacent sequences: A066754 A066755 A066756 * A066758 A066759 A066760 KEYWORD base,more,nonn AUTHOR Erich Friedman, Jan 17 2002 EXTENSIONS a(13)-a(15) from Lars Blomberg, May 18 2011 Description clarified and offset corrected by Lars Blomberg, May 29 2011 STATUS approved

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Last modified October 4 17:22 EDT 2023. Contains 365887 sequences. (Running on oeis4.)