A115708 Semiprimes (A001358) whose digit reversal is a pentagonal number (A000326).

10, 15, 21, 22, 235, 287, 517, 529, 671, 1513, 1555, 2611, 5137, 5331, 6241, 7017, 7171, 7421, 7597, 7814, 10078, 10913, 15011, 15094, 15214, 15251, 20395, 20603, 21542, 23129, 24501, 24873, 25157, 26851, 27161, 51998, 53297, 54989, 55551

Offset: 1

Author

Giovanni Resta, Jan 31 2006

Keywords

• nonn
• base

Examples

			235=5*47 is semiprime and 532 is the 19th pentagonal number.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A000326, A001358, A115709.

Programs

Mathematica

Select[Range[60000],PrimeOmega[#]==2&&IntegerQ[(1+Sqrt[1+24* IntegerReverse[#]])/ 6]&] (* Harvey P. Dale, Apr 27 2022 *)