OFFSET
0,2
COMMENTS
Cell configuration converges to a fractal with dimension 2.771...
LINKS
Colin Barker, Table of n, a(n) for n = 0..750
Peter Karpov, InvMem, Item 26
Peter Karpov, Illustration of initial terms (n = 1..4)
Index entries for linear recurrences with constant coefficients, signature (21).
FORMULA
a(0) = 1, a(1) = 18, a(n) = 21*a(n-1).
G.f.: (1-3*x)/(1-21*x).
a(n) = 2 * 3^(n+1) * 7^(n-1) for n>0. - Colin Barker, Apr 23 2017
E.g.f.: (1 + 6*exp(21*x))/7. - G. C. Greubel, Dec 09 2021
MATHEMATICA
{1}~Join~LinearRecurrence[{21}, {18}, 17]
PROG
(PARI) Vec((1-3*x) / (1-21*x) + O(x^20)) \\ Colin Barker, Apr 23 2017
(Sage) [1]+[18*21^(n-1) for n in (1..40)] # G. C. Greubel, Dec 09 2021
(Magma) [1] cat [18*21^(n-1): n in [1..40]]; // G. C. Greubel, Dec 09 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Peter Karpov, Apr 23 2017
STATUS
approved