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%I #16 Nov 11 2020 03:07:12
%S 1,1,4,27,16777216,437893890380859375,
%T 500702078263459319174537025249570888246709955377400223021257741084821677152403456
%N Ultradoublefactorials: a(n) = (n!!)^(n!!).
%C The next term (a(8)) has 993 digits. - _Harvey P. Dale_, Aug 17 2017
%F a(n) = A006882(n)^A006882(n).
%F Sum_{n>=1} 1/a(n) = A134877. - _Amiram Eldar_, Nov 11 2020
%e For n=4 the doublefactorial is n!! = 4*2 = 8 and a(n) = n!!^n!! = 8^8 = 16777216.
%p P:=proc(i) local a,n; for n from 0 by 1 to i do print(doublefactorial(n)^doublefactorial(n)); od; end: P(10);
%t udf[n_]:=Module[{c=n!!},c^c]; Array[udf,7,0] (* _Harvey P. Dale_, Aug 17 2017 *)
%Y Cf. A006882, A046882, A134877, A165812.
%K easy,nonn
%O 0,3
%A _Paolo P. Lava_ & _Giorgio Balzarotti_, Mar 16 2010
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