A086890 Imaginary part of Propp's cubic recurrence starting with i (i^2=-1).

1, 1, 1, 1, -1, -2, 0, -10, 29, -689, 79779, -306741785, -537059115735445, 32782820784889194174016393, 123899509182081496572342154385115870319926534, 6620488215208352146569523585853411114659592927465468100410366988520167986216

Offset: 1

Author

Benoit Cloitre, Sep 17 2003

Keywords

• sign

Comments

b(n)=x(n)+i*y(n) where x(n) and y(n) are integer sequences.

Crossrefs

Cf. A051786, A086889.

Formula

a(n)=Im(b(n)) where b(1)=b(2)=b(3)=b(4)=i and b(n)=(1+b(n-1)*b(n-2)*b(n-3))/b(n-4)