|
|
A010685
|
|
Period 2: repeat (1,4).
|
|
26
|
|
|
1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1, 4, 1
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
Continued fraction of (1 + sqrt(2))/2. - R. J. Mathar, Nov 21 2011
This sequence can be generated by an infinite number of formulas all having the form a^(b*n) mod c subject to the following conditions. The number a can be congruent to either 2,3, or 4 mod 5 (A047202). If a is congruent to 2 or 3 mod 5, then b can be any number of the form 4k+2 and c = 5 or 15. If a is congruent to 4 mod 5, then b can be any number of the form 2k+1 and c = 5. For example: a(n) = 29^(13*n) mod 5, a(n) = 24^(11*n) mod 5, and a(n) = 22^(10*n) mod 15. - Gary Detlefs, May 19 2014
|
|
LINKS
|
|
|
FORMULA
|
a(2n) = 1, a(2n+1) = 4.
G.f.: (1+4*x)/((1-x)*(1+x)).
E.g.f.: (5*exp(x) - 3*exp(-x))/2.
a(n) = (5 - 3*(-1)^n)/2.
a(n) = 4^((1-(-1)^n)/2) = 2^(1-(-1)^n) = 2/(2^((-1)^n)).
a(n) = 4^(ceiling(n/2) - floor(n/2)). (End)
a(n) = gcd((n-1)^2, (n+1)^2). - Paul Barry, Sep 16 2004
|
|
MAPLE
|
if type(n, 'even') then
1 ;
else
4;
end if;
|
|
MATHEMATICA
|
|
|
PROG
|
(Sage) [power_mod(4, n, 5)for n in range(0, 81)] # Zerinvary Lajos, Nov 26 2009
(PARI) values(m)=my(v=[]); for(i=1, m, v=concat([1, 4], v)); v; /* Anders Hellström, Aug 03 2015 */
(Magma) [Modexp(4, n, 5): n in [0..100]]; // G. C. Greubel, Nov 22 2021
|
|
CROSSREFS
|
Cf. sequences listed in Comments section of A283393.
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|