OFFSET
0,2
FORMULA
a(0) = 0 and a(1) = 2, a(n) = a(n-1) + 2 * (a(n-1)^5 - 4) mod 7^n for n > 1.
EXAMPLE
a(1) = ( 2)_7 = 2,
a(2) = ( 12)_7 = 9,
a(3) = ( 212)_7 = 107,
a(4) = (1212)_7 = 450.
PROG
(PARI) {a(n) = truncate((4+O(7^n))^(1/5))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Aug 03 2019
STATUS
approved