login
A121134
Numbers of isomers of unbranched a-4-catapolypentagons - see Brunvoll reference for precise definition.
1
1, 2, 5, 11, 30, 72, 182, 434, 1048, 2456, 5752, 13240, 30336, 68736, 154912, 346400, 770688, 1704576, 3753344, 8226176, 17959936, 39062528, 84679168, 182983168, 394278912, 847263744, 1816164352, 3883956224, 8288010240, 17649696768
OFFSET
2,2
REFERENCES
J. Brunvoll, S. J. Cyvin and B. N. Cyvin, Isomer enumeration of polygonal systems..., J. Molec. Struct. (Theochem), 364 (1996), 1-13.
FORMULA
G.f.: x*(8*x^9+4*x^8-18*x^7-10*x^6+20*x^5+8*x^4-13*x^3-x^2+4*x-1) / ((2*x-1)^3*(2*x^2-1)^2). - Colin Barker, Nov 30 2012
MAPLE
H := proc(r, alpha, q) local rhalf, alphahalf ; rhalf := floor(r/2) ; alphahalf := floor(alpha/2) ; (binomial(rhalf-1, alphahalf-1)*(q-3)+binomial(rhalf-1, alphahalf))*(q-3)^(rhalf-alphahalf-1) ; end: J := proc(r, alpha, q) (binomial(r-2, alpha-2)*(q-3)^2+2*binomial(r-2, alpha-1)*(q-3)+binomial(r-2, alpha))*(q-3)^(r-alpha-2) ; end: Ifunc := proc(r, alpha, q) J(r, alpha, q)/4+binomial(2, r-alpha)/4+ (1+(-1)^(r+alpha)+(1+(-1)^alpha)*(1-(-1)^r)/2)*H(r, alpha, q)/4 ; end: A121134 := proc(n) Ifunc(n, 2, 5) ; end: for n from 2 to 80 do printf("%d, ", A121134(n)) ; od: # R. J. Mathar, Aug 07 2008
CROSSREFS
Sequence in context: A272675 A059075 A345882 * A144959 A131347 A292210
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Aug 13 2006
EXTENSIONS
Extended beyond a(10) by R. J. Mathar, Aug 07 2008
STATUS
approved