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 A006580 a(n) = Sum_{k=1..n-1} lcm(k,n-k). (Formerly M3336) 3
 1, 4, 8, 20, 21, 56, 60, 96, 105, 220, 152, 364, 301, 360, 464, 816, 549, 1140, 760, 1036, 1221, 2024, 1196, 2200, 2041, 2484, 2184, 4060, 2205, 4960, 3664, 4224, 4641, 5180, 4008, 8436, 6517, 7072, 5980, 11480, 6321, 13244, 8888, 9540, 11661 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 REFERENCES Marc LeBrun, personal communication. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Reinhard Zumkeller, Table of n, a(n) for n = 2..1000 M. Le Brun, Email to N. J. A. Sloane, Jul 1991 MATHEMATICA Table[ Sum[ LCM[ k, n-k ], {k, 1, n-1} ], {n, 2, 50} ] (* Olivier Gérard, Aug 15 1997 *) PROG (Haskell) a006580 n = a006580_list !! (n-1) a006580_list = map sum a003990_tabl -- Reinhard Zumkeller, Aug 05 2012 (PARI) a(n) = sum(k=1, n-1, lcm(k, n-k)); \\ Michel Marcus, Aug 11 2017 CROSSREFS Antidiagonal sums of array A003990. Sequence in context: A273143 A273174 A178447 * A061814 A087254 A160726 Adjacent sequences:  A006577 A006578 A006579 * A006581 A006582 A006583 KEYWORD nonn,changed AUTHOR EXTENSIONS More terms from Olivier Gérard, Aug 15 1997 STATUS approved

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Last modified August 24 05:48 EDT 2017. Contains 291052 sequences.