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

1,1

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A001358, A115741.

Sequence in context: A301292 A359696 A134978 * A026102 A338024 A144519

Adjacent sequences: A115739 A115740 A115741 * A115743 A115744 A115745

Keyword

nonn,base

Author

Giovanni Resta, Jan 31 2006

Status

approved