|
|
A056284
|
|
Number of n-bead necklaces with exactly four different colored beads.
|
|
7
|
|
|
0, 0, 0, 6, 48, 260, 1200, 5106, 20720, 81876, 318000, 1223136, 4675440, 17815020, 67769552, 257700906, 980240880, 3731753180, 14222737200, 54278580036, 207438938000, 793940475900, 3043140078000, 11681057249536, 44900438149296, 172824331826580, 666070256489680
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,4
|
|
COMMENTS
|
Turning over the necklace is not allowed.
|
|
REFERENCES
|
M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]
|
|
LINKS
|
|
|
FORMULA
|
a(n) = (k!/n) Sum_{d|n} phi(d) S2(n/d,k), where k=4 is the number of colors and S2 is the Stirling subset number A008277.
G.f.: -Sum_{d>0} (phi(d)/d) * Sum_{j} (-1)^(k-j) * C(k,j) * log(1-j x^d), where k=4 is the number of colors. (End)
|
|
EXAMPLE
|
For n=4, the six necklaces are ABCD, ABDC, ACBD, ACDB, ADBC and ADCB.
|
|
MATHEMATICA
|
k=4; Table[k!DivisorSum[n, EulerPhi[#]StirlingS2[n/#, k]&]/n, {n, 1, 30}] (* Robert A. Russell, Sep 26 2018 *)
|
|
PROG
|
(PARI) a(n) = my(k=4); (k!/n)*sumdiv(n, d, eulerphi(d)*stirling(n/d, k, 2)); \\ Michel Marcus, Sep 27 2018
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|