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

 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 Andrew Howroyd, Table of n, a(n) for n = 1..200 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 Adjacent sequences: A330618 A330619 A330620 * A330622 A330623 A330624 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.

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