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 A121566 a(n) is the denominator of Sum_{i=1..n} i!/(i^2). 1
 1, 1, 2, 6, 3, 15, 15, 105, 105, 105, 105, 1155, 1155, 15015, 15015, 15015, 15015, 255255, 255255, 4849845, 4849845, 4849845, 4849845, 111546435, 111546435, 111546435, 111546435, 111546435, 111546435, 3234846615, 3234846615, 100280245065, 100280245065 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA Denominator of Sum_{i=1..n} A000142(i)/A000290(i). EXAMPLE n=0: the empty sum is 0 by convention, so a(0)=1. n=1: the sum is 1, so a(1)=1. n=2: the sum is 1 + 1/2 = 3/2 so a(2) = 2. MATHEMATICA Join[{1}, Accumulate[Table[n!/n^2, {n, 40}]]//Denominator] (* Harvey P. Dale, May 11 2019 *) PROG (PARI) a(n) = denominator(sum(i=1, n, i!/i^2)); \\ Michel Marcus, Mar 18 2018 CROSSREFS Cf. A121565 (numerator). Sequence in context: A094299 A304537 A330252 * A056839 A302033 A071301 Adjacent sequences:  A121563 A121564 A121565 * A121567 A121568 A121569 KEYWORD easy,frac,nonn AUTHOR Jonathan Vos Post, Aug 07 2006 STATUS approved

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Last modified June 2 14:21 EDT 2020. Contains 334787 sequences. (Running on oeis4.)