OFFSET
0
COMMENTS
arctan(x) = x - x^3/3 + x^5/5 - x^7/7 + ...
LINKS
Wikipedia, p-adic number
EXAMPLE
arctan(4) = ...0100000001010001001111101100100101000100.
PROG
(PARI) a(n) = lift(sum(i=0, (n-2)/4, Mod((-1)^i*4^(2*i+1)/(2*i+1), 2^(n+1))))\2^n
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jianing Song, Aug 16 2019
STATUS
approved