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%I #9 Jul 29 2017 13:59:09
%S 0,1,2,4,5,6,7,8,10,11,12,13,14,17,18,19,20,21,23,24,25,26,27,29,30,
%T 31,32,33,35,36,37,38,39,41,42,43,44,45,48,49,50,51,52,54,55,56,57,58,
%U 60,61,62,63,64,66,67,68,69,70,72,73,74,75,76,80,81,82,83,84,86,87,88,89,90,92,93
%N v_5( (10n)! ) - v_5( (5n)! ), where v_p(N) is the p-adic valuation defined in A112765.
%F a(n) - n = a( [(n+2)/5] ).
%p A127428 := proc(n)
%p padic[ordp]((10*n)!,5)-padic[ordp]((5*n)!,5) ;
%p end proc:
%p seq(A127428(n),n=0..100) ; # _R. J. Mathar_, Mar 29 2017
%o (PARI) a(n) = valuation((10*n)!, 5) - valuation((5*n)!, 5); \\ _Michel Marcus_, Jul 29 2017
%Y v_5(n) is given in A112765. Cf. A001511, A127427.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Apr 02 2007
%E Typo in name corrected by _Michel Marcus_, Jul 29 2017