A121479 Triangular numbers with more than three distinct prime factors.

210, 630, 780, 990, 1326, 1540, 1596, 1770, 1830, 2145, 2346, 2415, 2850, 2926, 3003, 3486, 3570, 3828, 4095, 4186, 4278, 4560, 4950, 5460, 5565, 6105, 6216, 6555, 6670, 6786, 7140, 7260, 7626, 8385, 8646, 8778, 9180, 9730, 9870, 10296, 10440, 10878

Offset: 1

Author

Klaus Brockhaus, Aug 01 2006

Keywords

• easy
• nonn

Examples

			20*21/2 = 2*3*5*7 = 210 is the smalles triangular number with more than three distinct prime factors, hence a(1) = 210.
		

Links

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

Crossrefs

Cf. A000217, A068443, A119663, A121478.

Programs

Mathematica

Select[Accumulate[Range[200]],PrimeNu[#]>3&] (* Harvey P. Dale, Jun 06 2013 *)

PARI

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