OFFSET
0,2
COMMENTS
x = ...526436,
x^2 = ...666661 = -6.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1183
Wikipedia, Hensel's Lemma.
FORMULA
a(0) = 0 and a(1) = 6, a(n) = a(n-1) + 4 * (a(n-1)^2 + 6) mod 7^n for n > 1.
If n > 0, a(n) = 7^n - A290800(n).
EXAMPLE
a(1) = 6_7 = 6,
a(2) = 36_7 = 27,
a(3) = 436_7 = 223,
a(4) = 6436_7 = 2281,
a(5) = 26436_7 = 7083.
PROG
(PARI) a(n) = if (n, 7^n - truncate(sqrt(-6+O(7^(n)))), 0)
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Aug 11 2017
STATUS
approved