1,1

S. Kitaev and T. Mansour, Counting the occurrences of generalized patterns....

a(1) = 3, a(n) = {3*4^(n-1) + 2^n}/2.

G.f.: [6-20x+8x^2]/[(1-2x)(1-4x)].

(PARI) a(n)=(3*4^(n-1)+2^n)/2

Sequence in context: A026627 A148866 A151431 this_sequence A135583 A009437 A000776

Adjacent sequences: A093353 A093354 A093355 this_sequence A093357 A093358 A093359

nonn

Ralf Stephan, Apr 27 2004