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%I #6 Oct 01 2013 17:58:01
%S 2,4,9,19,51,177,747,3638,19691,115237,716530,4675989,31744547,
%T 222714791,1606590368,11868687555,89506353843,687275943030,
%U 5361745095952,42423407975227,339921277226567,2754682467870463,22553369649557926,186375668569345609
%N Integer part of the fourth nesting of the logarithmic integral of 10^n.
%C m=4 in PARI below. With nesting level 7, z < 1 and Li(z) is not defined so an error occurs. This is why we take the absolute value of Li(z).
%F Let Li(n) = logarithmic integral of n. a(n) = Li(Li(Li(Li(n))))
%t Floor[Nest[LogIntegral,10^Range[30],4]] (* _Harvey P. Dale_, Jun 18 2013 *)
%o (PARI) g(n,m) = for(x=1,n,z=10^x;for(y=1,m,z=abs(Li(z)));print1(floor(z)",")) Li(x) = { -eint1(log(1/x)) }
%K nonn
%O 1,1
%A _Cino Hilliard_, Jun 30 2004
%E More terms from _Harvey P. Dale_, Jun 18 2013