login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A032094 Number of reversible strings with n-1 beads of 2 colors. 7 beads are black. String is not palindromic. 4
4, 16, 60, 160, 396, 848, 1716, 3200, 5720, 9696, 15912, 25152, 38760, 58080, 85272, 122496, 173052, 240240, 328900, 443872, 592020, 780208, 1017900, 1314560, 1682928, 2135744, 2689808, 3361920, 4173840, 5147328, 6310128, 7689984, 9321780, 11240400 (list; graph; refs; listen; history; text; internal format)
OFFSET

9,1

COMMENTS

If the offset is changed to 3, this is the 2nd Witt transform of A000292 [Moree]. - R. J. Mathar, Nov 08 2008

Also 7th column of A159916, i.e., number of 7-element subsets of {1,...,n-1} whose elements add up to an odd integer. - M. F. Hasler, May 02 2009

LINKS

Colin Barker, Table of n, a(n) for n = 9..1000

C. G. Bower, Transforms (2)

Pieter Moree, The formal series Witt transform, Discr. Math. no. 295 vol. 1-3 (2005) 143-160. - R. J. Mathar, Nov 08 2008

Index entries for linear recurrences with constant coefficients, signature (4,-2,-12,17,8,-28,8,17,-12,-2,4,-1).

FORMULA

"BHK[ 8 ]" (reversible, identity, unlabeled, 8 parts) transform of 1, 1, 1, 1...

G.f.: 4*x^9*(1+x^2)/((1-x)^8*(1+x)^4). a(n)=4*A031164(n-9). - R. J. Mathar, Nov 08 2008

From Colin Barker, Mar 07 2015: (Start)

a(n) = (n^7-28*n^6+322*n^5-1960*n^4+6664*n^3-11872*n^2+8448*n)/10080 if n is even.

a(n) = (n^7-28*n^6+322*n^5-1960*n^4+6769*n^3-13132*n^2+13068*n-5040)/10080 if n is odd.

(End)

PROG

(PARI) A032094(n)=(binomial(n--, 7)-if(n%2, binomial(n\2, 3)))\2 \\ M. F. Hasler, May 02 2009

(PARI) Vec(4*x^9*(1+x^2)/((1-x)^8*(1+x)^4) + O(x^100)) \\ Colin Barker, Mar 07 2015

CROSSREFS

Cf. A032091, A005995, A018210, A159916. - M. F. Hasler, May 02 2009

Sequence in context: A207276 A047123 A297096 * A282083 A261563 A265955

Adjacent sequences:  A032091 A032092 A032093 * A032095 A032096 A032097

KEYWORD

nonn,easy

AUTHOR

Christian G. Bower

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified February 24 06:13 EST 2018. Contains 299597 sequences. (Running on oeis4.)