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A260234
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Largest prime factor of the n-th hexagonal number (A000384).
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6
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3, 5, 7, 5, 11, 13, 5, 17, 19, 11, 23, 13, 7, 29, 31, 17, 7, 37, 13, 41, 43, 23, 47, 7, 17, 53, 11, 29, 59, 61, 7, 13, 67, 23, 71, 73, 19, 13, 79, 41, 83, 43, 29, 89, 23, 47, 19, 97, 11, 101, 103, 53, 107, 109, 37, 113, 29, 59, 17, 61, 41, 7, 127, 43, 131
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OFFSET
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2,1
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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a(3) = 5 because A000384(3) = 15 = 3 * 5.
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MATHEMATICA
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FactorInteger[#][[-1, 1]]&/@PolygonalNumber[6, Range[2, 70]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 10 2018 *)
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PROG
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(PARI)
pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
lpf(m) = vecmax(factorint(m)[, 1]) \\ Largest prime factor
a(n) = lpf(pg(6, n))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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