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A004154 Omit trailing zeros from factorial numbers. 10

%I

%S 1,1,2,6,24,12,72,504,4032,36288,36288,399168,4790016,62270208,

%T 871782912,1307674368,20922789888,355687428096,6402373705728,

%U 121645100408832,243290200817664,5109094217170944,112400072777760768

%N Omit trailing zeros from factorial numbers.

%H Reinhard Zumkeller, <a href="/A004154/b004154.txt">Table of n, a(n) for n = 0..250</a>

%H <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>

%F a(n) = A000142(n) / 10^A027868(n). - _Reinhard Zumkeller_, Nov 24 2012

%F a(n+1) = A004151((n+1)*a(n)). - _Reinhard Zumkeller_, Nov 24 2012, corrected by _M. F. Hasler_, Oct 16 2014

%F a(n) = A004151(A000142(n)) = A000142(n)/A011557(A112765(n)), or A122840 instead of A112765. - _M. F. Hasler_, Oct 16 2014

%t f[n_] := n!/10^Sum[Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Table[f[n], {n, 0, 22}]

%o (Haskell)

%o a004154 = a004151 . a000142

%o a004154_list = scanl (\u v -> a004151 $ u * v) 1 [1..]

%o -- _Reinhard Zumkeller_, Nov 24 2012

%o (PARI) a(n)=n!/10^valuation(n!,5) \\ _M. F. Hasler_, Oct 16 2014

%o (MAGMA) [Factorial(n)/10^Valuation(Factorial(n), 5): n in [0..30]]; // _Vincenzo Librandi_, Oct 16 2014

%Y Cf. A000142, A004151.

%K nonn,base

%O 0,3

%A _N. J. A. Sloane_.

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Last modified August 10 07:37 EDT 2020. Contains 336368 sequences. (Running on oeis4.)