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A328823
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a(n) is the least prime factor of A000096(n) = n*(n+3)/2.
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1
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2, 5, 3, 2, 2, 3, 5, 2, 2, 5, 7, 2, 2, 7, 3, 2, 2, 3, 11, 2, 2, 5, 13, 2, 2, 13, 3, 2, 2, 3, 17, 2, 2, 17, 5, 2, 2, 19, 3, 2, 2, 3, 23, 2, 2, 7, 5, 2, 2, 5, 3, 2, 2, 3, 5, 2, 2, 29, 31, 2, 2, 5, 3, 2, 2, 3, 5, 2, 2, 5, 37, 2, 2, 7, 3, 2, 2
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OFFSET
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1,1
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COMMENTS
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The motivation is that n*(n+3)/2 = n + T(n), where T(n) = n*(n+1)/2 = A000217(n), the triangular numbers.
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LINKS
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FORMULA
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EXAMPLE
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For n = 5, n + T(n) = 5 + 15 = 20. The smallest prime factor of 20 is 2, so a(5) = 2.
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MATHEMATICA
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Array[FactorInteger[# (# + 3)/2][[1, 1]] &, 77] (* Amiram Eldar, Nov 02 2019 *)
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PROG
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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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