

A121479


Triangular numbers with more than three distinct prime factors.


2



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
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OFFSET

1,1


LINKS

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


EXAMPLE

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


MATHEMATICA

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


PROG

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


CROSSREFS

Cf. A000217, A068443, A119663, A121478.
Sequence in context: A306508 A254466 A235304 * A235921 A236432 A118279
Adjacent sequences: A121476 A121477 A121478 * A121480 A121481 A121482


KEYWORD

easy,nonn


AUTHOR

Klaus Brockhaus, Aug 01 2006


STATUS

approved



