A309724 - OEIS

A309724

Digits of the 8-adic integer (1/7)^(1/7).

7, 0, 5, 4, 4, 7, 7, 4, 1, 6, 1, 3, 3, 0, 3, 4, 5, 0, 5, 4, 2, 7, 5, 3, 1, 4, 7, 6, 0, 6, 1, 2, 4, 6, 2, 2, 1, 6, 2, 0, 2, 5, 1, 6, 3, 4, 0, 6, 1, 2, 4, 0, 5, 6, 5, 5, 0, 4, 6, 7, 5, 4, 0, 0, 1, 6, 3, 6, 7, 6, 1, 2, 7, 2, 3, 3, 7, 1, 5, 5, 4, 6, 3, 4, 6, 1, 3, 3, 3, 2, 6, 1, 4, 3, 0, 0, 1, 4, 4, 5, 4

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OFFSET

0,1

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..10000

Wikipedia, Hensel's Lemma.

FORMULA

Define the sequence {b(n)} by the recurrence b(0) = 0 and b(1) = 7, b(n) = b(n-1) + 7 * (7 * b(n-1)^7 - 1) mod 8^n for n > 1, then a(n) = (b(n+1) - b(n))/8^n.

PROG

(PARI) N=100; Vecrev(digits(lift((1/7+O(2^(3*N)))^(1/7)), 8), N)

(Ruby)

def A309724(n)

ary = [7]

a = 7

n.times{|i|

b = (a + 7 * (7 * a ** 7 - 1)) % (8 ** (i + 2))

ary << (b - a) / (8 ** (i + 1))

a = b

}

ary