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A208185
Number of distinct n-colored necklaces with 4 beads per color.
2
1, 1, 10, 2896, 3941598, 15277017432, 135277939358160, 2374127830286012160, 74701932179186551241520, 3911393168902074440088524160, 321715999535364496261149134365440, 39702971502659332476270701578180454400, 7081620512071831837127802029303335215878400
OFFSET
0,3
LINKS
FORMULA
a(n) = Sum_{d|4} phi(4/d)*(n*d)!/(d!^n*n*4) if n>0 and a(0) = 1.
For n > 0, a(n) = (4*n)!/(4*n*24^n) + (n-1)!/2 + (2*n-1)!/2^(n+1). - Vaclav Kotesovec, Aug 23 2015
EXAMPLE
a(0) = 1: the empty necklace.
a(1) = 1: {0000}.
a(2) = 10: {00001111, 00010111, 00100111, 01000111, 00011011, 00110011, 00101011, 01010011, 01001011, 01010101}.
MAPLE
with(numtheory);
a:= n-> `if`(n=0, 1, add(phi(4/d) *(n*d)!/(d!^n *4*n), d={1, 2, 4})):
seq(a(n), n=0..15);
MATHEMATICA
Flatten[{1, Table[(4*n)!/(4*n*24^n) + (n-1)!/2 + (2*n-1)!/2^(n+1), {n, 1, 15}]}] (* Vaclav Kotesovec, Aug 23 2015 *)
CROSSREFS
Row n=4 of A208183.
Sequence in context: A246116 A132675 A227223 * A123377 A061543 A305666
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 24 2012
STATUS
approved