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A081257
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a(n) is the greatest prime factor of (n^3 - 1).
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8
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7, 13, 7, 31, 43, 19, 73, 13, 37, 19, 157, 61, 211, 241, 13, 307, 17, 127, 421, 463, 13, 79, 601, 31, 37, 757, 271, 67, 29, 331, 151, 1123, 397, 97, 43, 67, 1483, 223, 547, 1723, 139, 631, 283, 109, 103, 61, 181, 43, 2551, 379, 919, 409, 2971, 79, 103, 3307, 163
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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(7)=19 because 7^3 - 1 = 342 = 2*3*3*19.
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MAPLE
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MATHEMATICA
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FactorInteger[#][[-1, 1]]&/@(Range[2, 60]^3-1) (* Harvey P. Dale, Oct 09 2017 *)
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PROG
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(Python)
from sympy import primefactors
def A081257(n): return max(primefactors(n-1)+primefactors(n*(n+1)+1)) # Chai Wah Wu, Oct 15 2022
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CROSSREFS
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Cf. A096175 (n^3-1 is an odd semiprime), A096176 ((n^3-1)/(n-1) is prime).
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KEYWORD
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easy,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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