|
|
A048840
|
|
Expansion of (1 - x + 2*x^2 + 2*x^3 - x^4 - x^5)/(1-x)^3.
|
|
3
|
|
|
1, 2, 5, 12, 22, 34, 48, 64, 82, 102, 124, 148, 174, 202, 232, 264, 298, 334, 372, 412, 454, 498, 544, 592, 642, 694, 748, 804, 862, 922, 984, 1048, 1114, 1182, 1252, 1324, 1398, 1474, 1552, 1632, 1714, 1798, 1884, 1972, 2062, 2154, 2248, 2344, 2442, 2542
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
Also, number of permutations of length n+1 which avoid the patterns 321, 1342, 2134. - Lara Pudwell, Feb 26 2006
|
|
LINKS
|
|
|
FORMULA
|
For n > 2, a(n) = n^2 + 3n - 6.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 5. - Colin Barker, May 03 2019
|
|
MATHEMATICA
|
CoefficientList[Series[(1-x+2*x^2+2*x^3-x^4-x^5)/(1-x)^3, {x, 0, 60}], x] (* or *) Join[{1, 2, 5}, Table[n^2+3*n-6, {n, 3, 60}]] (* or *) Join[{1, 2, 5}, LinearRecurrence[{3, -3, 1}, {12, 22, 34}, 58]] (* Vladimir Joseph Stephan Orlovsky, Jan 31 2012 *)
|
|
PROG
|
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|