A066758 Triangular numbers not divisible by 10 whose reverse is pentagonal.

0, 1, 15, 21, 62481, 67896, 2618616, 10095771, 10550121, 5491258003, 103352174628, 299536839001, 7220385308804403, 7686108558349885, 10917127849295955, 724804915074540097006

Offset

1,3

Links

Table of n, a(n) for n=1..16.

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, r]; Print[A]]]

Crossrefs

Sequence in context: A307792 A236764 A300958 * A338119 A297931 A018888

Adjacent sequences: A066755 A066756 A066757 * A066759 A066760 A066761

Keyword

base,more,nonn

Author

Erich Friedman, Jan 17 2002

Extensions

a(13)-a(16) from Lars Blomberg, May 18 2011

Description clarified and offset corrected by Lars Blomberg, May 29 2011

Status

approved