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 A245972 Tower of 5s mod n. 9
 0, 1, 2, 1, 0, 5, 3, 5, 2, 5, 1, 5, 5, 3, 5, 5, 14, 11, 6, 5, 17, 1, 5, 5, 0, 5, 2, 17, 9, 5, 25, 21, 23, 31, 10, 29, 35, 25, 5, 5, 9, 17, 28, 1, 20, 5, 23, 5, 45, 25, 14, 5, 51, 29, 45, 45, 44, 9, 48, 5, 14, 25, 38, 53, 5, 23, 5, 65, 5, 45, 1, 29, 34, 35, 50 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n) = (5^(5^(5^(5^(5^ ... ))))) mod n, provided sufficient 5s are in the tower such that adding more doesn't affect the value of a(n). LINKS Wayne VanWeerthuizen, Table of n, a(n) for n = 1..10000 FORMULA a(n) = 5^a(A000010(n)) mod n. For n<=18, a(n)=(5^5) mod n. EXAMPLE a(2) = 1, as 5^X is odd for any whole number X. a(19) = 6, as 5^(5^5) == 5^(5^(5^5)) == 5^(5^(5^(5^5))) == 6 (mod 19). MAPLE A:= proc(n) option remember; 5 &^ A(numtheory:-phi(n)) mod n end proc: A(2):= 1; seq(A(n), n=2..100); PROG (Sage) def a(n):     if ( n <= 18 ):         return 3125%n     else:         return power_mod(5, a(euler_phi(n)), n) CROSSREFS Cf. A240162, A245970, A245971, A245973, A245974. Sequence in context: A327358 A256664 A226783 * A088391 A128899 A155887 Adjacent sequences:  A245969 A245970 A245971 * A245973 A245974 A245975 KEYWORD nonn,easy AUTHOR Wayne VanWeerthuizen, Aug 08 2014 STATUS approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)