OFFSET
0,3
LINKS
Paul D. Hanna, Table of n, a(n) for n = 0..1000
EXAMPLE
G.f.: A(x) = 1 + x + 3*x^2 + 5*x^3 + 9*x^4 + 19*x^5 + 25*x^6 + 59*x^7 +...
The terms equal the norm of the complex coefficients in the expansion:
1/(1-x-2*I*x^2) = 1 + x + (1 + 2*I)*x^2 + (1 + 4*I)*x^3 + (-3 + 6*I)*x^4 + (-11 + 8*I)*x^5 + (-23 + 2*I)*x^6 + (-39 - 20*I)*x^7 + (-43 - 66*I)*x^8 + (-3 - 144*I)*x^9 + (129 - 230*I)*x^10 + (417 - 236*I)*x^11 + (877 + 22*I)*x^12 +...
so that
a(1) = 1, a(2) = 1 + 2, a(3) = 1 + 4, a(4) = 3 + 6, a(5) = 11 + 8, ...
PROG
(PARI) {a(n)=local(Cn=polcoeff(1/(1-x-2*I*x^2+x*O(x^n)), n)); abs(real(Cn)) + abs(imag(Cn))}
for(n=0, 40, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Oct 21 2012
STATUS
approved