A245971 Tower of 4s mod n.

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

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