%I #14 Jun 22 2021 01:01:57
%S 18,33,44,57,71,102,105,128,170,173,188,204,253,296,309,316,322,382,
%T 453,499,502,538,543,547,588,590,622,638,705,733,739,744,774,809,816,
%U 822,846,854,892,936,957,970,973,995,998,1004,1055,1092,1099,1117,1131
%N Numbers whose factorial has '28' as its final two digits before the trailing zeros.
%H Charles R Greathouse IV, <a href="/A045556/b045556.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>
%o (PARI) last(n,k)=if(n*8\9-1<k, n=n!; return(n/10^valuation(n,10)%10^k)); my(m=Mod(1,5^k)); for(i=2,n,m*=i/10^valuation(i,5));lift(chinese(m, Mod(0,2^k))) \\ Gives the last k decimal digits of n!.
%o is(n)=last(n,2)==28 \\ _Charles R Greathouse IV_, Oct 22 2014
%o (PARI) is(n)=my(m=Mod(1,25)); for(i=2,n, m*=i/10^valuation(i,5)); m==28 \\ _Charles R Greathouse IV_, Oct 22 2014
%o (PARI) v=List();m=Mod(1,25);for(n=2,1e6,m*=n/10^valuation(n,5);if(m==28,listput(v,n);if(#v==100, return(Vec(v))))) \\ _Charles R Greathouse IV_, Oct 22 2014
%K nonn,base
%O 1,1
%A _Jeff Burch_
%E More terms from _Robert G. Wilson v_, Dec 14 2000