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%I #9 Apr 24 2015 11:27:56
%S 1,3,3,60,60,201,481,5989,3122037,4434429,13576837,183894465,
%T 187925171,209072257,1498642520,12239200420,20220712468,20220712468,
%U 875023683404,992997544772,2721798771116,9770941874212,9770941874212
%N a(n) starts arithmetic progression of n terms separated by tau(a(n)), each term having the same number of divisors
%C a(15) > 10^9.
%C a(19) > 10^11. - _Donovan Johnson_, Sep 24 2009
%C a(24) > 10^13. - _Giovanni Resta_, Aug 02 2013
%e tau(60) = tau(72) = tau(84) = tau(96) = tau(108) = 12. This is the first such progression of length greater than 3, so a(4) and a(5) are both 60.
%o (PARI) has(n)=my(t=numdiv(n),s=1); while(numdiv(n+=t)==t, s++); s
%o a(n)=my(k); while(has(k++)<n,); k \\ _Charles R Greathouse IV_, Apr 24 2015
%Y Cf. A064491, A165498, A165499.
%K hard,nonn,more
%O 1,2
%A _Hugo van der Sanden_, Sep 21 2009
%E a(15)-a(18) from _Donovan Johnson_, Sep 24 2009
%E a(19)-a(23) from _Giovanni Resta_, Aug 02 2013
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