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 A333378 a(n) = F(n) * (-1)^(n*(n-1)/2) where F(n) = A000045(n) Fibonacci numbers. 1
 0, 1, -1, -2, 3, 5, -8, -13, 21, 34, -55, -89, 144, 233, -377, -610, 987, 1597, -2584, -4181, 6765, 10946, -17711, -28657, 46368, 75025, -121393, -196418, 317811, 514229, -832040, -1346269, 2178309, 3524578, -5702887, -9227465, 14930352, 24157817, -39088169 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS This is a strong elliptic divisibility sequence t_n as given in [Kimberling, p. 16] where x = -1, y = -2, z = -3. The Hankel transform of -A026726(n+k) is a(2*n+2+k) for k = 0, 1. Let a(n) := F(n) * (-1)^binom(n, 2). Then a(m - n) * a(m + n) = a(m + 1) * a(m - 1) * a(n)^2 - a(n + 1) * a(n - 1) * a(m)^2. This plus gcd(f[n], f[m]) = |f[gcd(n, m)]| makes a[] a strong elliptic divisibility sequence. Likewise F(n) * (-1)^binom(n - 1, 2), but no other asSIGNation (mod scaling). - Bill Gosper, May 28 2008 LINKS Clark Kimberling, Strong divisibility sequences and some conjectures, Fib. Quart., 17 (1979), 13-17. Index to sequences with linear recurrences with constant coefficients, signature (0,-3,0,-1). FORMULA G.f.: (x^3 - x^2 + x)/(x^4 + 3*x^2 + 1). a(n) = -a(-n) = -3*a(n+2) -a(n+4) for all n in Z. 0 = a(n)^2 -a(n+1)^2 +a(n+2)^2 +2*a(n)*a(n+2) for all n in Z. 0 = a(n)*(+a(n+2)) +a(n+1)*(+a(n+1) +a(n+3)) +a(n+2)*(+a(n+2)) for all n in Z. 0 = a(n)*a(n+4) - a(n+1)*a(n+3) - 2*a(n+2)^2 for all n in Z. 0 = a(n)*a(n+5) + 2*a(n+1)*a(n+4) - 3*a(n+2)*a(n+3) for all n in Z. a(n+1) = i^(n^2) * U(n, i/2) for all n in Z [From Gosper, Mar 19 2020]. - Michael Somos, Mar 19 2020 EXAMPLE G.f. = x - x^2 - 2*x^3 + 3*x^4 + 5*x^5 - 8*x^6 - 13*x^7 + 21*x^8 + ... MATHEMATICA a[ n_] := Fibonacci[n] (-1)^(n (n - 1) / 2); a[ n_] := With[{m=n-1}, I^m^2 ChebyshevU[m, I/2]]; (* Michael Somos, Mar 19 2020 *) PROG (PARI) {a(n) = fibonacci(n) * (-1)^(n*(n-1)/2)}; (Sage) def A333378():     a, b, c, d = False, True, True, False     x, y = 0, 1     while True:         yield x if a else -x         x, y = y, x - y         a, b, c, d = b, c, d, a a = A333378() print([next(a) for _ in range(39)]) # Peter Luschny, Mar 19 2020 CROSSREFS Cf. A000045, A026726. Sequence in context: A152163 A039834 A236191 * A000045 A324969 A020695 Adjacent sequences:  A333375 A333376 A333377 * A333379 A333380 A333381 KEYWORD sign,easy AUTHOR Michael Somos, Mar 17 2020 STATUS approved

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Last modified September 24 20:13 EDT 2020. Contains 337321 sequences. (Running on oeis4.)