OFFSET
1,1
EXAMPLE
11*12/2 = 2*3*11 = 66 is the smalles triangular number with three distinct prime factors, hence a(1) = 66.
MATHEMATICA
Select[Accumulate[Range[0, 100]] , PrimeNu[#]==3&] (* James C. McMahon, Oct 19 2024 *)
PROG
(PARI) for(n=1, 100, k=binomial(n+1, 2); if(omega(k)==3, print1(k, ", ")))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Klaus Brockhaus, Aug 01 2006
STATUS
approved