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 A245971 Tower of 4s mod n. 9
 0, 0, 1, 0, 1, 4, 4, 0, 4, 6, 4, 4, 9, 4, 1, 0, 1, 4, 9, 16, 4, 4, 3, 16, 21, 22, 13, 4, 24, 16, 4, 0, 4, 18, 11, 4, 34, 28, 22, 16, 37, 4, 41, 4, 31, 26, 17, 16, 11, 46, 1, 48, 47, 40, 26, 32, 28, 24, 45, 16, 57, 4, 4, 0, 61, 4, 55, 52, 49, 46, 50, 40, 37 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS a(n) = (4^(4^(4^(4^(4^ ... ))))) mod n, provided sufficient 4s 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 PROG (Sage) def tower4mod(n):     if n <= 10:         return 256%n     else:         ep = euler_phi(n)         return power_mod(4, ep+tower4mod(ep), n) [tower4mod(n) for n in range(1, 30)] (Haskell) import Math.NumberTheory.Moduli (powerMod) a245971 n = powerMod 4 (phi + a245971 phi) n             where phi = a000010 n -- Reinhard Zumkeller, Feb 01 2015 CROSSREFS Cf. A240162, A245970, A245972, A245973, A245974. Cf. A000010, A000302. Sequence in context: A290799 A155836 A337398 * A279365 A164613 A104794 Adjacent sequences:  A245968 A245969 A245970 * A245972 A245973 A245974 KEYWORD nonn,easy AUTHOR Wayne VanWeerthuizen, Aug 08 2014 STATUS approved

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Last modified July 29 12:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)