OFFSET
0,2
COMMENTS
[Empirical] a(base,n)=a(base-1,n)+A002426(n+1) for base>=1.int(n/2)+1.
a(n) = T(n, 12) where T(n, k) = Sum_{j=1..k} (1+2*cos(j*Pi/(k+1)))^n. These are the number of smooth cyclic words of length n over the alphabet {1,2,..,12}. See theorem 3.3 in Knopfmacher and others, reference in A124696. - Peter Luschny, Aug 13 2012
FORMULA
G.f.: (1 - 55*x^2 + 220*x^3 - 135*x^4 - 672*x^5 + 1050*x^6 + 216*x^7 - 1015*x^8 + 160*x^9 + 270*x^10 - 40*x^11 - 11*x^12) / ((1 - 5*x + 5*x^2 + 6*x^3 - 7*x^4 - 2*x^5 + x^6)*(1 - 7*x + 15*x^2 - 6*x^3 - 11*x^4 + 6*x^5 + x^6)) (conjectured). - Colin Barker, Jul 17 2017
PROG
(S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-1](($[i]`-$[(i+1)mod N]`>1)+($[(i+1)mod N]`-$[i]`>1))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
R. H. Hardin, Dec 28 2006
STATUS
approved