A115742 - OEIS

%I #4 Nov 14 2013 09:04:46

%S 6,15,28,55,78,105,120,190,496,780,903,946,1176,1225,1275,1540,1653,

%T 1770,1830,1891,2080,3081,3403,3486,3570,3741,3916,4186,4753,5050,

%U 5356,5671,6670,7021,7140,7381,7503,7626,8515,8911,9316,9591,9870

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

%H Harvey P. Dale, <a href="/A115742/b115742.txt">Table of n, a(n) for n = 1..1000</a>

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

%t Select[Accumulate[Range[200]],PrimeOmega[FromDigits[Reverse[ IntegerDigits[ #]]]] == 2&] (* _Harvey P. Dale_, Nov 14 2013 *)

%Y Cf. A001358, A115741.

%K nonn,base

%O 1,1

%A _Giovanni Resta_, Jan 31 2006