

A119663


Triangular numbers with at most two distinct prime factors.


3



1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 91, 136, 153, 171, 253, 325, 351, 496, 703, 1081, 1225, 1431, 1711, 1891, 2701, 3321, 3403, 4753, 5671, 7381, 8128, 12403, 13203, 13861, 15931, 18721, 25651, 29161, 29403, 31375, 32896, 34453, 38503, 49141
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OFFSET

1,2


COMMENTS

1 and 3 are the only terms with less than two prime factors.


LINKS



EXAMPLE

a(6) = 3 * 7, a(7) = 2^2 * 7, a(8) = 2^2 * 3^2.


PROG

(PARI) for(n=1, 320, k=binomial(n+1, 2); if(omega(k)<=2, print1(k, ", ")))  (Klaus Brockhaus, Jul 30 2006)


CROSSREFS



KEYWORD

easy,nonn


AUTHOR



EXTENSIONS



STATUS

approved



