|
|
A280569
|
|
a(n) = (-1)^n * 2 if n = 5*k and n!=0, otherwise a(n) = (-1)^n.
|
|
0
|
|
|
1, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1, -2, 1, -1, 1, -1, 2, -1, 1, -1, 1
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,6
|
|
LINKS
|
|
|
FORMULA
|
Euler transform of length 10 sequence [-1, 1, 0, 0, -1, -1, 0, 0, 0, 1].
a(n) = -b(n) where b() is multiplicative with b(2^e) = -1 if e>0, b(5^e) = 2 if e>0, b(p^e) = 1 otherwise.
G.f.: (1 - x + x^2) * (1 - x^3) / (1 + x^5).
G.f.: 1 - x / (1 + x) - x^5 / (1 + x^5).
a(n) = a(-n) for all n in Z.
a(5*n) = A280560(n) for all n in Z.
|
|
EXAMPLE
|
G.f. = 1 - x + x^2 - x^3 + x^4 - 2*x^5 + x^6 - x^7 + x^8 - x^9 + 2*x^10 + ...
|
|
MATHEMATICA
|
a[ n_] := (-1)^n If[ n != 0 && Divisible[n, 5], 2, 1];
LinearRecurrence[{0, 0, 0, 0, -1}, {1, -1, 1, -1, 1, -2}, 120] (* or *) PadRight[ {1}, 120, {2, -1, 1, -1, 1, -2, 1, -1, 1, -1}] (* Harvey P. Dale, Jul 18 2021 *)
|
|
PROG
|
(PARI) {a(n) = (-1)^n * if(n && n%5==0, 2, 1)};
(PARI) {a(n) = n=abs(n); polcoeff( (1 - x + x^2) * (1 - x^3) / (1 + x^5) + x * O(x^n), n)};
(Magma) m:=75; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1 - x+x^2)*(1-x^3)/(1+x^5))); // G. C. Greubel, Jul 29 2018
|
|
CROSSREFS
|
|
|
KEYWORD
|
sign
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|