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A245971
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Tower of 4s mod n.
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9
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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
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OFFSET
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1,6
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COMMENTS
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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).
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LINKS
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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