A121479 - OEIS

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

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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: A358988 A254466 A235304 * A235921 A236432 A118279

Adjacent sequences: A121476 A121477 A121478 * A121480 A121481 A121482

KEYWORD

easy,nonn

AUTHOR

Klaus Brockhaus, Aug 01 2006

STATUS

approved