A309605 Digits of the 10-adic integer (61/9)^(1/3).

9, 0, 5, 0, 5, 4, 7, 1, 9, 1, 6, 0, 9, 8, 5, 7, 1, 0, 7, 3, 1, 0, 9, 5, 1, 4, 9, 9, 5, 7, 9, 3, 0, 1, 1, 9, 0, 1, 4, 1, 4, 0, 6, 4, 4, 1, 8, 0, 0, 1, 7, 6, 9, 1, 5, 3, 8, 1, 4, 2, 6, 7, 1, 3, 3, 9, 8, 0, 4, 5, 3, 7, 2, 5, 2, 7, 5, 5, 4, 6, 1, 0, 0, 2, 2, 3, 2, 0, 7, 3, 4, 2, 7, 7, 1, 0, 3, 1, 0, 9

Offset

0,1

Links

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

Formula

Define the sequence {b(n)} by the recurrence b(0) = 0 and b(1) = 9, b(n) = b(n-1) + 7 * (9 * b(n-1)^3 - 61) mod 10^n for n > 1, then a(n) = (b(n+1) - b(n))/10^n.

Example

       9^3 == 9      (mod 10).
       9^3 == 29     (mod 10^2).
     509^3 == 229    (mod 10^3).
     509^3 == 2229   (mod 10^4).
   50509^3 == 22229  (mod 10^5).
  450509^3 == 222229 (mod 10^6).

Prog

(PARI) N=100; Vecrev(digits(lift(chinese(Mod((61/9+O(2^N))^(1/3), 2^N), Mod((61/9+O(5^N))^(1/3), 5^N)))), N)
(Ruby)
def A309605(n)
  ary = [9]
  a = 9
  n.times{|i|
    b = (a + 7 * (9 * a ** 3 - 61)) % (10 ** (i + 2))
    ary << (b - a) / (10 ** (i + 1))
    a = b
  }
  ary
end
p A309605(100)

Crossrefs

Cf. A309600, A309643.

Sequence in context: A361061 A301865 A370705 * A010770 A021921 A374751

Adjacent sequences: A309602 A309603 A309604 * A309606 A309607 A309608

Keyword

nonn

Author

Seiichi Manyama, Aug 09 2019

Status

approved