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%I #14 May 19 2021 16:05:10
%S 0,2,2,4,16,256,65536,4294967296,18446744073709551616,
%T 340282366920938463463374607431768211456,
%U 115792089237316195423570985008687907853269984665640564039457584007913129639936
%N Number of children at height n in a doubly logarithmic tree. Leaves are at height 0.
%H Vincenzo Librandi, <a href="/A171163/b171163.txt">Table of n, a(n) for n = 0..13</a>
%H Omer Berkman, Baruch Schieber and Uzi Vishkin, <a href="https://doi.org/10.1006/jagm.1993.1018">Optimal doubly logarithmic parallel algorithms based on finding all nearest smaller values</a>, Journal of Algorithms, 14(1993)(3): 344-370.
%F a(0)=0, a(1)=2; for n>1, a(n) = 2^(2^(n-2)).
%t Join[{0, 2}, Table[2^2^(n-2), {n, 2, 9}]] (* _Harvey P. Dale_, Feb 01 2014 *)
%o (Python)
%o def doubly_log_tree_children(n):
%o if n==0:
%o return 0
%o if n==1:
%o return 2
%o return 2**(2**(n-2))
%Y Equals A001146 with the prefix 0, 2.
%Y Cf. A165420. [_R. J. Mathar_, Dec 11 2009]
%K nonn
%O 0,2
%A _Chad Brewbaker_, Dec 04 2009
%E More terms from _Harvey P. Dale_, Feb 01 2014
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