A115707 Pentagonal numbers (A000326) whose digit reversal is a prime.

5, 35, 70, 92, 145, 376, 1520, 1820, 3577, 3725, 7526, 9322, 9560, 10045, 10292, 13490, 14065, 16801, 17767, 18760, 32782, 34126, 34580, 36895, 38320, 38801, 39772, 73151, 74482, 76501, 78547, 91390, 93625, 94376, 98176, 100492, 101270

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

145 is the 10th pentagonal number and 541 is prime.

Mathematica

Select[Table[n (3n-1)/2, {n, 400}], PrimeQ[FromDigits[Reverse[ IntegerDigits[ #]]]]&]  (* Harvey P. Dale, Feb 23 2011 *)
Select[PolygonalNumber[5, Range[300]], PrimeQ[IntegerReverse[#]]&] (* Harvey P. Dale, Mar 27 2024 *)

Crossrefs

Cf. A000326, A115706.

Sequence in context: A014632 A117985 A371561 * A117793 A145920 A356179

Adjacent sequences: A115704 A115705 A115706 * A115708 A115709 A115710

Keyword

nonn,base

Author

Giovanni Resta, Jan 31 2006

Status

approved