login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A330621 Number of length n bracelets with entries covering an initial interval of positive integers and no adjacent entries equal. 2
0, 1, 1, 7, 27, 207, 1689, 17137, 196869, 2556856, 36878013, 585247590, 10131891315, 190024056601, 3838053182983, 83057105368627, 1917217162193175, 47021314781221603, 1221073517359584357, 33471097453271690668, 965771726172667547339, 29259595679585441629303 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
EXAMPLE
Case n=4: there are the following 7 bracelets:
1212,
1213, 1232, 1323,
1234, 1243, 1324.
PROG
(PARI) \\ here U(n, k) is A208544(n, k) for n > 1.
U(n, k) = (sumdiv(n, d, eulerphi(n/d)*(k-1)^d)/n + if(n%2, 1-k, k*(k-1)^(n/2)/2))/2;
a(n)={if(n<1, n==0, sum(j=1, n, U(n, j)*sum(k=j, n, (-1)^(k-j)*binomial(k, j))))}
CROSSREFS
Row sums of A330341.
Cf. A208544.
Sequence in context: A192250 A035081 A193257 * A173193 A196323 A003148
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Dec 20 2019
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 4 22:06 EST 2024. Contains 370532 sequences. (Running on oeis4.)