|
Search: id:A117887
|
|
|
| A117887 |
|
Number of labeled trees on <= n nodes. |
|
+0
2
|
|
| 1, 4, 20, 145, 1441, 18248, 280392, 5063361, 105063361, 2463011052, 64380375276, 1856540769313, 58550453144609, 2004745521503984, 74062339559431920, 2936485391069247713, 124376016487663499489, 5604762874272465685428
(list; graph; listen)
|
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
A000178 = SUM[k=1..n] k^(k-1). A001923 = SUM[k=1..n] k^k. A061789 = SUM[k=1..n] p(k)^p(k), p(k) = k-th prime. a(n) = number of spanning trees in complete graphs K_i on i <= n labeled nodes. Also is partial sum of counts of parking functions, noncrossing partitions, critical configurations of the chip firing game, allowable pairs sorted by a priority queue. a(14) = 58550453144609 is prime.
|
|
FORMULA
|
a(n) = SUM[k=2..n] k^(k-2). a(n) = SUM[k=2..n] A000272(k).
|
|
CROSSREFS
|
Cf. A000178, A000272, A001923, A061789.
Adjacent sequences: A117884 A117885 A117886 this_sequence A117888 A117889 A117890
Sequence in context: A098541 A004204 A034216 this_sequence A082988 A001171 A094070
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Jonathan Vos Post (jvospost2(AT)yahoo.com), May 03 2006
|
|
|
Search completed in 0.002 seconds
|
