OFFSET
0
COMMENTS
arctan(x) = x - x^3/3 + x^5/5 - x^7/7 + ...
LINKS
Wikipedia, p-adic number
EXAMPLE
arctan(2) = ...0101100110111010110101111110001011001010.
PROG
(PARI) a(n) = lift(sum(i=0, (n-1)/2, Mod((-1)^i*2^(2*i+1)/(2*i+1), 2^(n+1))))\2^n
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jianing Song, Aug 15 2019
STATUS
approved