OFFSET
0,3
COMMENTS
This is a generalized Somos-4 sequence. - Michael Somos, Mar 14 2020
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..114
FORMULA
a(n) = (-2)^floor(C(n+1,2)/2) = (-2)^A011848(n+1).
0 = a(n)*a(n+4) - 2*a(n+1)*a(n+3) + 4*a(n+2)^2 = a(n)*a(n+5) - 4*a(n+1)*a(n+4) for all n in Z. - Michael Somos, Mar 14 2020
MATHEMATICA
Table[(-2)^Floor[Binomial[n + 1, 2]/2], {n, 0, 50}] (* G. C. Greubel, May 03 2018 *)
a[ n_] := (-2)^Quotient[n (n + 1), 4]; (* Michael Somos, Mar 14 2020 *)
PROG
(PARI) for(n=0, 50, print1((-2)^floor(binomial(n+1, 2)/2), ", ")) \\ G. C. Greubel, May 03 2018
(Magma) [(-2)^Floor(Binomial(n+1, 2)/2): n in [0..50]]; // G. C. Greubel, May 03 2018
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, May 21 2009
STATUS
approved