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A119663
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Triangular numbers with at most two distinct prime factors.
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3
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 1 and 3 are the only terms with less than two prime factors.
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LINKS
| Klaus Brockhaus, Table of n, a(n) for n=1..1000
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EXAMPLE
| a(6) = 3 * 7, a(7) = 2^2 * 7, a(8) = 2^2 * 3^2.
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PROG
| (PARI) for(n=1, 320, k=binomial(n+1, 2); if(omega(k)<=2, print1(k, ", "))) - (Klaus Brockhaus, Jul 30 2006)
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CROSSREFS
| Cf. A000217, A068443, A005384.
Sequence in context: A069696 A025724 A025746 * A025715 A165145 A046489
Adjacent sequences: A119660 A119661 A119662 * A119664 A119665 A119666
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KEYWORD
| easy,nonn
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AUTHOR
| Greg Huber (huber(AT)alum.mit.edu), Jul 28 2006
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EXTENSIONS
| More terms from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Jul 30 2006 and May 21 2008
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