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%I #41 Feb 13 2024 13:15:19
%S 1,1,2,6,24,12,72,504,4032,36288,36288,399168,4790016,62270208,
%T 871782912,1307674368,20922789888,355687428096,6402373705728,
%U 121645100408832,243290200817664,5109094217170944,112400072777760768,2585201673888497664,62044840173323943936
%N a(n) = n! with trailing zeros omitted.
%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
%p a:= n-> (f-> f/10^padic[ordp](f,10))(n!):
%p seq(a(n), n=0..29); # _Alois P. Heinz_, Dec 29 2021
%t Array[#!//.x_/;x~Mod~5==0:>x/10&,22] (* _Giorgos Kalogeropoulos_, Aug 17 2020 *)
%t Join[{1,1,2,6,24},Table[FromDigits[Flatten[Most[Split[IntegerDigits[n!]]]]],{n,5,30}]] (* or *) Table[n!/10^IntegerExponent[n!,10],{n,0,30}] (* _Harvey P. Dale_, Feb 13 2024 *)
%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, A008904 (mod 10).
%K nonn,base
%O 0,3
%A _N. J. A. Sloane_
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