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A069902
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Largest prime factor of n-th triangular number n(n+1)/2.
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5
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3, 3, 5, 5, 7, 7, 3, 5, 11, 11, 13, 13, 7, 5, 17, 17, 19, 19, 7, 11, 23, 23, 5, 13, 13, 7, 29, 29, 31, 31, 11, 17, 17, 7, 37, 37, 19, 13, 41, 41, 43, 43, 11, 23, 47, 47, 7, 7, 17, 17, 53, 53, 11, 11, 19, 29, 59, 59, 61, 61, 31, 7, 13, 13, 67
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| a(n) = A006530(A000217(n)).
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EXAMPLE
| A000217(9) = 9*(9+1)/2 = 55 = 3*3*5, therefore a(9) = 5.
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MATHEMATICA
| PrimeFactors[n_]:=Flatten[Table[ #[[1]], {1}]&/@FactorInteger[n]]; Table[PrimeFactors[n*(n-1)/2][[ -1]], {n, 3, 6!}] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 12 2009]
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CROSSREFS
| Cf. A069901, A069903, A069904. Essentially the same as A074399.
Sequence in context: A110560 A141424 A172170 * A085779 A078936 A061794
Adjacent sequences: A069899 A069900 A069901 * A069903 A069904 A069905
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KEYWORD
| nonn
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 10, 2002
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