A066741 Pentagonal numbers not divisible by 10 whose reverse is a square.

0, 1, 925, 1426, 6112, 9801, 140301, 52244922262, 1445531162626, 5205252778462, 63253297234426, 9040940929621480310251

Offset: 1

Author

Erich Friedman, Jan 16 2002

Keywords

• base
• more
• nonn

Comments

a(13) > 2^63. - Donovan Johnson, May 24 2011

Examples

			925 is pentagonal and 529 is square.
		

Crossrefs

Cf. A000290, A000326, A067251.

Programs

Mathematica

dtn[L_] := Fold[10#1+#2&, 0, L] A={0}; For[i=1, i>0, i++, t=i(3i-1)/2; r=dtn[Reverse[IntegerDigits[t]]]; If[IntegerQ[Sqrt[r]]&&Mod[t, 10]>0, AppendTo[A, t]; Print[A]]]

Extensions

a(12) from Donovan Johnson, Apr 03 2008

Offset corrected by Donovan Johnson, May 24 2011

Description clarified and a(12) corrected by Lars Blomberg, May 29 2011