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A245974 Tower of 7's mod n. 8
0, 1, 1, 3, 3, 1, 0, 7, 7, 3, 2, 7, 6, 7, 13, 7, 12, 7, 7, 3, 7, 13, 20, 7, 18, 19, 16, 7, 1, 13, 19, 23, 13, 29, 28, 7, 34, 7, 19, 23, 26, 7, 7, 35, 43, 43, 37, 7, 0, 43, 46, 19, 11, 43, 13, 7, 7, 1, 7, 43, 6, 19, 7, 55, 58, 13, 63, 63, 43, 63, 66, 7, 30 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = (7^(7^(7^(7^(7^ ... ))))) mod n, provided sufficient 7's 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) = 7^a(A000010(n)) mod n. For n <= 10, a(n) = (7^7) mod n.

EXAMPLE

a(2) = 1, as 7^X is odd for any whole number X.

a(11) = 2, as 7^(7^7) == 7^(7^(7^7)) == 7^(7^(7^(7^7))) == 2 (mod 11).

MAPLE

A:= proc(n) option remember; 7 &^ A(numtheory:-phi(n)) mod n end proc:

A(2):= 1;

seq(A(n), n=2..100);

PROG

(Sage)

def a(n):

    if ( n <= 10 ):

        return 823543%n

    else:

        return power_mod(7, a(euler_phi(n)), n)

CROSSREFS

Cf. A240162, A245970, A245971, A245972, A245973.

Sequence in context: A261634 A295848 A226785 * A316989 A135009 A092747

Adjacent sequences:  A245971 A245972 A245973 * A245975 A245976 A245977

KEYWORD

nonn,easy

AUTHOR

Wayne VanWeerthuizen, Aug 08 2014

STATUS

approved

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Last modified July 7 15:49 EDT 2020. Contains 335495 sequences. (Running on oeis4.)