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Search: id:A121479
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| A121479 |
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Triangular numbers with more than three distinct prime factors. |
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+0
2
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| 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
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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20*21/2 = 2*3*5*7 = 210 is the smalles triangular number with more than three distinct prime factors, hence a(1) = 210.
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PROGRAM
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(PARI) for(n=1, 100, k=binomial(n+1, 2); if(omega(k)>3, print1(k, ", ")))
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CROSSREFS
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Cf. A000217, A068443, A119663, A121478.
Sequence in context: A046386 A046402 A147571 this_sequence A118279 A163263 A009127
Adjacent sequences: A121476 A121477 A121478 this_sequence A121480 A121481 A121482
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KEYWORD
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easy,nonn
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 01 2006
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