

A089264


Number of permutations of length n containing exactly once 132 and 213, likewise for pattern pair (231,312).


1



3, 6, 17, 42, 102, 242, 564, 1296, 2944, 6624, 14784, 32768, 72192, 158208, 345088, 749568, 1622016, 3497984, 7520256, 16121856, 34471936, 73531392, 156499968, 332398592, 704643072, 1491075072, 3149922304, 6643777536, 13992198144
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OFFSET

4,1


LINKS



FORMULA

For n>=7, a(n) = (n^2+21*n28)*2^(n9).
G.f.: x^4*(x1)^2*(2*x^32*x^2+6*x3) / (2*x1)^3. [Colin Barker, Jan 31 2013]


MATHEMATICA

LinearRecurrence[{6, 12, 8}, {3, 6, 17, 42, 102, 242}, 40] (* Harvey P. Dale, Apr 10 2022 *)


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



