OFFSET
1,2
LINKS
FORMULA
a(n) = 2*a(n-1) - 5*a(n-2), n>3.
a(n) = left term in [1,-2; 2,1]^n * [1,1].
a(n) = (1/2)*(1+i)*((1+2*i)^n-i*(1-2*i)^n), where i=sqrt(-1). - Bruno Berselli, Jul 06 2011
EXAMPLE
a(5) = 79 = 2*a(4) - 5*a(3) = 2*17 - 5*(-9).
a(5) = 79 = left term in [1,-2, 2,1]^5.
PROG
(PARI) a(n)={local(v=Vec((1+2*I*x)^n)); sum(k=1, #v, real(v[k])-imag(v[k])); } /* cf. A116483 */ /* Joerg Arndt, Jul 06 2011 */
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Gary W. Adamson, Mar 28 2008
STATUS
approved