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A076551
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Smallest triangular number with n prime factors (counted without multiplicity).
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12
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1, 3, 6, 66, 210, 3570, 103740, 930930, 56812470, 1722580860, 32395433070, 265257422430, 91348974206490, 8923863379851420, 330196858581850260, 14193386885746698630, 2378522762792139793830, 351206814022419685159830, 28791787439593010836313310
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OFFSET
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0,2
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COMMENTS
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a(19) <= 8285055066500101241048306610. a(20) <= 120052594044654305809137933570. - Donovan Johnson, Feb 28 2012
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LINKS
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EXAMPLE
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a(0) = 1 because 1 is a triangular number with zero prime factors; a(3) = 66 because 66 = 2*3*11 is a triangular number with 3 distinct prime factors.
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PROG
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(PARI) {n=12; v=vector(n); for(k=1, 1000000, t=k*(k+1)/2; d=1+omega(t); if(d<=n&&v[d]<1, v[d]=t)); for(j=1, n, print1(v[j], ", "))}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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