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a(n) = Sum_{k=1..n} k!^k!.
1

%I #12 Oct 24 2024 14:18:04

%S 1,5,46661,1333735776850284124449081472890437

%N a(n) = Sum_{k=1..n} k!^k!.

%C The next term has 250 digits. - _Harvey P. Dale_, Dec 19 2014

%t s=0;lst={};Do[AppendTo[lst,s+=n!^n! ],{n,1,6,1}];lst

%t Accumulate[Table[(k!)^k!,{k,5}]] (* _Harvey P. Dale_, Dec 19 2014 *)

%o (PARI) a(n)=sum(k=1,n,k!^k!) \\ _Charles R Greathouse IV_, Oct 12 2009

%Y Cf. A165710.

%K nonn

%O 1,2

%A _Vladimir Joseph Stephan Orlovsky_, Sep 24 2009