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A199423 Greatest prime factor of n and 2*n+1 2
3, 5, 7, 3, 11, 13, 7, 17, 19, 7, 23, 5, 13, 29, 31, 11, 17, 37, 19, 41, 43, 11, 47, 7, 17, 53, 11, 19, 59, 61, 31, 13, 67, 23, 71, 73, 37, 19, 79, 5, 83, 17, 43, 89, 13, 31, 47, 97, 11, 101, 103, 13, 107, 109, 37, 113, 23, 29, 59, 11, 61, 31, 127, 43, 131, 19 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = A006530(A014105(n)).
MATHEMATICA
Table[Max[Flatten[FactorInteger[{n, 2 n+1}], 1][[All, 1]]], {n, 70}] (* Harvey P. Dale, Mar 25 2020 *)
PROG
(PARI) gpf(n)=local(ps); if(n<2, n, ps=factor(n)[, 1]~; ps[#ps])
vector(80, n, gpf(n*(2*n+1)))
CROSSREFS
Sequence in context: A088836 A076565 A286517 * A100029 A099984 A130141
KEYWORD
nonn,easy
AUTHOR
STATUS
approved

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Last modified February 22 09:09 EST 2024. Contains 370250 sequences. (Running on oeis4.)