|
Search: id:A093374
|
|
|
| A093374 |
|
Number of 1-2-3-avoiding permutations with exactly thrice the 1-3-2 pattern. |
|
+0
1
|
|
| 1, 5, 18, 57, 168, 472, 1280, 3376, 8704, 22016, 54784, 134400, 325632, 780288, 1851392, 4354048, 10158080, 23527424, 54132736, 123797504, 281542656, 637009920, 1434451968, 3215982592, 7180648448, 15971909632, 35399925760
(list; graph; listen)
|
|
|
OFFSET
|
4,2
|
|
|
LINKS
|
D. Callan, A recursive bijective approach to counting permutations...
|
|
FORMULA
|
a(n) = C(n-3, 1)2^(n-4) + C(n-3, 1)2^(n-5) + C(n-3, 2)2^(n-7); for n<4, a(n) = 0.
G.f.: x^3(1-3x+2x^2+x^3)/(1-2x)^4.
|
|
PROGRAM
|
(PARI) a(n)=if(n<4, 0, 2^(n-4)*binomial(n-3, 1)+2^(n-5)*binomial(n-3, 2)+2^(n-7)*binomial(n-4, 3))
|
|
CROSSREFS
|
Sequence in context: A011845 A099450 A001793 this_sequence A000745 A128553 A000340
Adjacent sequences: A093371 A093372 A093373 this_sequence A093375 A093376 A093377
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Ralf Stephan, Apr 28 2004
|
|
|
Search completed in 0.005 seconds
|
