A115742 Triangular numbers whose digit reversal is a semiprime (A001358).

6, 15, 28, 55, 78, 105, 120, 190, 496, 780, 903, 946, 1176, 1225, 1275, 1540, 1653, 1770, 1830, 1891, 2080, 3081, 3403, 3486, 3570, 3741, 3916, 4186, 4753, 5050, 5356, 5671, 6670, 7021, 7140, 7381, 7503, 7626, 8515, 8911, 9316, 9591, 9870

Offset: 1

Author

Giovanni Resta, Jan 31 2006

Keywords

• nonn
• base

Examples

			15=T(5) and 51=3*17 is semiprime.
		

Links

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

Crossrefs

Cf. A001358, A115741.

Programs

Mathematica

Select[Accumulate[Range[200]],PrimeOmega[FromDigits[Reverse[ IntegerDigits[ #]]]] == 2&] (* Harvey P. Dale, Nov 14 2013 *)