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 A067391 a(n) is the least common multiple of numbers in {1,2,3,...,n-1} which do not divide n. 3
 1, 1, 2, 3, 12, 20, 60, 210, 840, 504, 2520, 27720, 27720, 51480, 360360, 180180, 720720, 4084080, 12252240, 232792560, 232792560, 21162960, 232792560, 5354228880, 5354228880, 2059318800, 26771144400, 80313433200, 80313433200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 FORMULA Let f(n) = lcm(1, 2, ..., n-1) = A003418(n-1). If n = 2*p^k for some prime p, then a(n) = f(n)/p; otherwise a(n) = f(n). EXAMPLE n=10: non-divisors = {3,4,6,7,8,9}, lcm(3,4,6,7,8,9) = 8*9*7 = 504 = a(10). For n=18, a(n) = lcm(4,5,7,8,10,11,12,13,14,15,16,17) = 4084080. MATHEMATICA a[n_] := LCM@@Select[Range[1, n-1], Mod[n, # ]!=0& ] Join[{1, 1}, Table[LCM@@Complement[Range[n], Divisors[n]], {n, 3, 30}]] (* Harvey P. Dale, Mar 27 2013 *) PROG (Haskell) a067391 n | n <= 2    = 1           | otherwise = foldl lcm 1 \$ a173540_row n -- Reinhard Zumkeller, Apr 04 2012 CROSSREFS Cf. A049820 [count], A007978 [min], A024816 [sum], A055067 [product]. Cf. A003418, A066574, A038610. Cf. A173540. Sequence in context: A319404 A126292 A083265 * A096361 A105045 A205825 Adjacent sequences:  A067388 A067389 A067390 * A067392 A067393 A067394 KEYWORD nonn AUTHOR Labos Elemer, Jan 22 2002 STATUS approved

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Last modified October 21 11:24 EDT 2019. Contains 328294 sequences. (Running on oeis4.)