1,2

M. Albert, M. Atkinson, and V. Vatter, Counting 1324-, 4231-avoiding permutations

G.f.: (1-12*x+59*x^2-152*x^3+218*x^4-168*x^5+58*x^6-6*x^7)/(1-x)/(1-2*x)^4/(1-4*x+2* x^2)

There are 22 permutations of length 4 which avoid these two patterns, so a(4)=22.

Sequence in context: A165525 A165526 A165527 this_sequence A116709 A165529 A116710

Adjacent sequences: A165525 A165526 A165527 this_sequence A165529 A165530 A165531

nonn

Vince Vatter (vatter(AT)gmail.com), Sep 21 2009