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%I #4 Mar 30 2012 18:39:24
%S 1,1,5,5,5,5,1,5,5,5,5,5,25,5,5,5,5,25,25,5,5,5,25,25,25,5,5,25,25,25,
%T 25,1,5,5,5,5,5,25,5,5,5,5,25,25,5,5,5,25,25,25,5,5,25,25,25,25,5,25,
%U 25,25,25,25,125,5,5,5,5,25,25,5,5,5,25,25,25,5,5,25,25,25,25,5,25,25,25
%N Denominator of (4n+1)!/5^n.
%F for n>=1, a(25n)=a(25n+1)=a(5n) ; a(25n+2)=a(25n+3)=a(25n+4)=a(25n+5)=5a(5n) ; a(25n+6)=a(n) ; a(25n+7)=a(25n+8)=a(25n+9)=a(25n+10)=a(25n+11)=5a(n) ; a(25n+12)=25a(n) ; a(25n+13)=a(25n+14)=a(25n+15)=a(25n+16)=a(5n+3) ; a(25n+17)=a(25n+18)=5a(5n+3) ; a(25n+19)=a(25n+20)=a(25n+21)=a(5n+4) ; a(25n+22)=a(25n+23)=a(25n+24)=5a(5n+4)
%o (PARI) a(n)=denominator((4*n+1)!/5^n)
%K nonn,frac
%O 0,3
%A _Benoit Cloitre_, Jan 01 2007
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