A121478 Triangular numbers with three distinct prime factors.

66, 78, 105, 120, 190, 231, 276, 300, 378, 406, 435, 465, 528, 561, 595, 666, 741, 820, 861, 903, 946, 1035, 1128, 1176, 1275, 1378, 1485, 1653, 1953, 2016, 2080, 2211, 2278, 2485, 2556, 2628, 2775, 3081, 3160, 3240, 3655, 3741, 3916, 4005, 4371, 4465

Offset: 1

Author

Klaus Brockhaus, Aug 01 2006

Keywords

• easy
• nonn

Examples

			11*12/2 = 2*3*11 = 66 is the smalles triangular number with three distinct prime factors, hence a(1) = 66.
		

Crossrefs

Cf. A000217, A068443, A119663, A121479.

Programs

Mathematica

Select[Accumulate[Range[0, 100]] ,PrimeNu[#]==3&] (* James C. McMahon, Oct 19 2024 *)

PARI

for(n=1,100,k=binomial(n+1,2);if(omega(k)==3,print1(k,",")))