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) = 3, b(n) = b(n-1) + 3 * (9 * b(n-1)^3 + 7) mod 10^n for n > 1, then a(n) = (b(n+1) - b(n))/10^n. - Seiichi Manyama, Aug 13 2019
EXAMPLE
3^3 == 7 (mod 10).
53^3 == 77 (mod 10^2).
753^3 == 777 (mod 10^3).
753^3 == 7777 (mod 10^4).
60753^3 == 77777 (mod 10^5).
660753^3 == 777777 (mod 10^6).
MAPLE
b:= proc(n) option remember; `if`(n<2, 3*n,
irem(b(n-1)+3*(9*b(n-1)^3+7), 10^n))
end:
a:= n-> (b(n+1)-b(n))/10^n:
seq(a(n), n=0..100); # Alois P. Heinz, Apr 14 2022
PROG
(PARI) n=0; for(i=1, 100, m=7*(10^i-1)/9; for(x=0, 9, if(((n+(x*10^(i-1)))^3)%(10^i)==m, n=n+(x*10^(i-1)); print1(x", "); break)))
(PARI) N=100; Vecrev(digits(lift(chinese(Mod((-7/9+O(2^N))^(1/3), 2^N), Mod((-7/9+O(5^N))^(1/3), 5^N)))), N) \\ Seiichi Manyama, Aug 05 2019
(Ruby)
def A225401(n)
ary = [3]
a = 3
n.times{|i|
b = (a + 3 * (9 * a ** 3 + 7)) % (10 ** (i + 2))
ary << (b - a) / (10 ** (i + 1))
a = b
}
ary
end
p A225401(100) # Seiichi Manyama, Aug 13 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Aswini Vaidyanathan, May 07 2013
STATUS
approved