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%I #28 Feb 10 2022 22:53:23
%S 6,9,8,8,2,7,1,1,4,0,9,2,5,5,5,2,0,3,2,2,6,3,9,4,9,5,3,1,4,3,9,3,1,2,
%T 0,6,5,7,5,6,3,4,2,1,3,5,2,6,0,6,2,9,5,4,0,6,6,0,7,5,9,5,6,9,0,6,1,4,
%U 6,8,8,3,8,3,6,4,8,8,0,5,2,3,0,3,2,6,2,5,4,1,1,1,9,0,9,8,0,8,1,4,3,1,0,1,8
%N Unique sequence of digits a(0), a(1), a(2), ... such that for all k >= 2, the number A(k) := Sum_{n = 0..k-1} a(n)*10^n satisfies 4^A(k) == A(k) (mod 10^k).
%C 10-adic expansion of the iterated exponential 4^^n for sufficiently large n (where c^^n denotes a tower of c's of height n). E.g., for n > 9, 4^^n == 1728896 (mod 10^7).
%D M. Ripà, La strana coda della serie n^n^...^n, Trento, UNI Service, Nov 2011, p. 69-78. ISBN 978-88-6178-789-6.
%D Ilan Vardi, "Computational Recreations in Mathematica," Addison-Wesley Publishing Co., Redwood City, CA, 1991, pages 226-229.
%H Robert G. Wilson v, <a href="/A133614/b133614.txt">Table of n, a(n) for n = 0..1024</a>
%H J. Jimenez Urroz and J. Luis A. Yebra, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL12/Yebra/yebra4.html">On the equation a^x == x (mod b^n)</a>, J. Int. Seq. 12 (2009) #09.8.8.
%e 698827114092555203226394953143931206575634213526062954066075956906146883836488...
%t (* Import Mmca coding for "SuperPowerMod" and "LogStar" from text file in A133612 and then *) $RecursionLimit = 2^14; f[n_] := SuperPowerMod[4, n + 1, 10^n]; Reverse@ IntegerDigits@ f@ 105 (* _Robert G. Wilson v_, Mar 06 2014 *)
%Y Cf. A133612, A133613, A133615, A133616, A133617, A133618, A133619, A144539, A144540, A144541, A144542, A144543, A144544.
%K nonn,base
%O 0,1
%A Daniel Geisler (daniel(AT)danielgeisler.com), Dec 18 2007
%E More terms from J. Luis A. Yebra, Dec 12 2008
%E Edited by _N. J. A. Sloane_, Dec 22 2008
%E a(68) onward from _Robert G. Wilson v_, Mar 06 2014
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