  We argue that the AdS/CFT calculational prescription for double-trace
deformations leads to a holographic derivation of the conformal anomaly, and
its conformal primitive, associated to the whole family of conformally
covariant powers of the Laplacian (GJMS operators) at the conformal boundary.
The bulk side involves a quantum 1-loop correction to the SUGRA action and the
boundary counterpart accounts for a sub-leading term in the large-N limit. The
sequence of GJMS conformal Laplacians shows up in the two-point function of the
CFT operator dual to a bulk scalar field at certain values of its scaling
dimension. The restriction to conformally flat boundary metrics reduces the
bulk computation to that of volume renormalization which renders the universal
type A anomaly. In this way, we directly connect two chief roles of the
Q-curvature: the main term in Polyakov formulas on one hand, and its relation
to the Poincare metrics of the Fefferman-Graham construction, on the other
hand. We find agreement with previously conjectured patterns including a
generic and simple formula for the type A anomaly coefficient that matches all
reported values in the literature concerning GJMS operators, to our knowledge.
