OFFSET
0,2
COMMENTS
Equals the self-convolution cube of the signed Thue-Morse sequence A106400: [1, -1, -1, 1, -1, 1, 1, -1, ...].
Conjecture: a(3*n) == A001285(n) (mod 3) for n >= 0, where A001285 is the Thue-Morse sequence: [1, 2, 2, 1, 2, 1, 1, 2, ...].
Conjecture: a(3*n+1) and a(3*n+2) are divisible by 3 for n >= 0.
LINKS
Paul D. Hanna, Table of n, a(n) for n = 0..16400
FORMULA
EXAMPLE
G.f.: A(x) = 1 - 3*x + 8*x^3 - 9*x^4 + 3*x^5 + 8*x^6 - 24*x^7 + 15*x^8 + 19*x^9 - 24*x^10 + 17*x^12 - 27*x^13 + 64*x^15 - 57*x^16 - 21*x^17 + 64*x^18 + ...
where A(x) = (1-x)^3 * (1-x^2)^3 * (1-x^4)^3 * (1-x^8)^3 * (1-x^16)^3 * ...
Notice that a(n) = 0 at n = [2, 11, 14, 47, 50, 59, 62, 191, 194, 203, 206, 239, 242, 251, 254, 767, ...] which appears to equal 3*A000695(k) - 1 for k >= 1.
PROG
(PARI) {a(n) = my(A = prod(k=0, #binary(n), (1 - x^(2^k))^3 +x*O(x^n))); polcoeff(A, n)}
for(n=0, 60, print1(a(n), ", "))
CROSSREFS
KEYWORD
sign,look
AUTHOR
Paul D. Hanna, Jun 20 2024
STATUS
approved