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 A352012 a(n) = Sum_{p|n, p prime} (n-1)!/(p-1)!. 5
 0, 1, 1, 6, 1, 180, 1, 5040, 20160, 378000, 1, 59875200, 1, 6235669440, 47221574400, 1307674368000, 1, 533531142144000, 1, 126713646259200000, 1219830034655232000, 51090956251003468800, 1, 38778025108327464960000, 25852016738884976640000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Table of n, a(n) for n=1..25. FORMULA E.g.f.: -Sum_{p prime} log(1-x^p)/p!. a(n) = 1 if and only if n is prime. MATHEMATICA a[1] = 0; a[n_] := (n - 1)! * Plus @@ (1/(FactorInteger[n][[;; , 1]] - 1)!); Array[a, 25] (* Amiram Eldar, Mar 01 2022 *) PROG (PARI) a(n) = sumdiv(n, d, isprime(d)*(n-1)!/(d-1)!); (PARI) my(N=40, x='x+O('x^N)); concat(0, Vec(serlaplace(-sum(k=1, N, isprime(k)*log(1-x^k)/k!)))) (PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, (n-1)!/(f[k, 1]-1)!); \\ Michel Marcus, Mar 01 2022 CROSSREFS Cf. A087906, A352004, A352014. Sequence in context: A352058 A303675 A266302 * A183284 A224476 A123147 Adjacent sequences: A352009 A352010 A352011 * A352013 A352014 A352015 KEYWORD nonn AUTHOR Seiichi Manyama, Feb 28 2022 STATUS approved

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Last modified May 18 15:59 EDT 2024. Contains 372664 sequences. (Running on oeis4.)